Difference between revisions of "Engine"

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[[Category: Internal Combustion]]
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The '''engine''' is the center of the internal combustion powertrain system. All other components of the greater system exist to service the engine in different ways. This means the engine is sensitive to design changes made across the entire powertrain. As of 2022, the FSAE rules require an internal combustion engine with a displacement of 710cc or less<ref>2022 fsae rules PDF: https://www.fsaeonline.com/cdsweb/gen/DownloadDocument.aspx?DocumentID=25e8885c-7397-4b2d-93b3-fc404960bab1</ref>. Available OEM motors within this displacement limit are largely sourced from motorcycles and snowmobiles. The purpose of the engine is to convert the chemical energy in [[Fuel|gasoline]] or [[Fuel|ethanol]] into mechanical energy used to propel the car. The engine is one of the most complicated and often heaviest single parts of any vehicle.
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==System design and engine choice==
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{{Main|List of Engines}}
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<!--
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Design of engine system: to buy or build, control, modifications.
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-->
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When designing the engine subsystem, the critical choice is to buy an engine or build a custom solution. Due to their complexity, both in design and manufacturing, most teams purchase an engine off the shelf. Once an engine has been selected, the engine itself will require a suite of accessory systems to run. "Engine tuning" is almost always referring to the tuning of these accessory systems such as fuel and spark timing. However, even if buying an engine, many options are available to teams to customize or modify the engine in order to optimize performance for team goals.
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''Wikipedia does a very detailed explanation on general engine layout so that will not be covered here.''
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The competition limits engine choice to a four-stroke, piston engine. The four strokes (intake, compression, power, exhaust) can be remembered by the crass pneumonic [[Otto Cycle|"suck, squeeze, bang, blow"]]. Rotary engines have competed in the past but were banned due to difficulty legislating displacement restrictions compared to a conventional piston engine. Most of the engines used in FS/FSAE are adapted from small personal vehicles such as motorcycles and snowmobiles.
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===Motorcycle engines===
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Motorcycle engines make up the vast majority  of engines used in FS/FSAE. The structure and operation of motorcycle engines differ from typical car engines in a few key places such as size, layout, and red line, etc. The two most common bike engine types used are
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# 600cc 4 cylinders weighing between 100-150 lbs (45-70kg) and producing about 125-140hp stock
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# Single cylinder 450cc engines typically that weigh in the neighborhood of 70-90 pounds (30-40kg)
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These engines are almost exclusively overhead cam layout.
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====Four cylinder engines====
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<!--Explain why you would choose a 4 cyl engine-->
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These bike engines are supersport engines and already configured to power a motorcycle in the same weight range as most FS/FSAE cars at a high level. These are easily adapted to use in a FSAE vehicle with modifications to the ancillary systems. The reliability and lower cost of these engines make them the most common choice in modern FSAE competitions. A 4 cylinder design smooths air flow through the restrictor as well as power delivery to the drive sprocket. The higher number of cylinders drives a more complicated [[Intake|intake]] and [[Exhaust|exhaust]] design. Additionally, the larger size and greater weight means packaging the engines may be more difficult than a smaller engine. The complexity of the engine internals may be a hurdle for servicing and in turn may drive rebuild issues if not done carefully. 4 cylinder engines in competition frequently see power figures in the 60-80hp range. Because of their higher power, cars that run these engines usually have a higher power to weight ratio than cars that run a single cylinder engine, despite the weight increase. These engines are also quite cheap, since you can buy engines from crashed bikes for not a lot of money (and usually the only thing damaged is the side covers).
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====Three cylinder engines====
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This category exists mostly because of Triumph's 675cc Daytona and Street Triple engines. They can provide similar power with less complexity than the four cylinder engines. They also have a higher displacement than any of the four cylinder engines.
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====Two cylinder engines====
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While rarer, some teams run two cylinder engines. Both V-twin and parallel twin engines exist in FSAE sizes. They generally lie somewhere between singles and four cylinders in terms of pros and cons. They may not make the same amount of power as the four cylinder engines but they are smoother than the single cylinder engines and less complex than the four cylinder engines.
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====Single cylinder engines====
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<!--Explain why you would choose a 1 cyl engine-->
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Single cylinder engines generally come from bikes built for motocross or on a motocross platform such as the Yamaha YZ450. These engines are lighter, and their reduced size makes packaging the engine and the ancillary systems much easier. The size and low weight of these engines allow them to be carried by a person without too much difficulty, easing transportation.
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The single cylinder results in a more dramatic pulsed flow through the intake restrictor making it more difficult for these engines to reach the high hp figures reached by a 4 cylinder engine. However the simplicity of the engine, intake, and exhaust system makes these engines a prime target for turbocharging which not only smooths out the pulsed flow, but also allows these to reach power figures in the same range as a naturally aspirated 4 cylinder or higher.
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Some designs such as the Yamaha YZ450F have the intake port in the front and the exhaust port in the back making exhaust routing even easier as it does not need to pass between the engine and the driver<ref>https://www.wheelsinmotionmc.com/inventory/v1/Current/Yamaha/Motorcycle/Cross-Country/WR450F/Base--Chatsworth-California---19488751?format=print</ref>.
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<!--
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crossflow cylinder discussion?
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-->
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===Snowmobile engines===
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If you have used a snowmobile engine, please help us by adding what you/your team has done to implement the engine in an FSAE context.
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===Other engines===
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Beyond the motorcycle and snowmobile engines, some teams go to more exotic design solutions, some even designing or using a custom engine.
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====Custom engines====
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Driven by either extreme performance goals, or academic pursuit, there is a history of custom FSAE engines. Most of these use or adapt internals from a motorcycle engine such as the pistons, or crankshaft, within a custom billet crankcase. However, with industry involvement, such as in the case of the Mahle or AMG engines, an entirely custom design can be utilized. Few of the custom engines remain in use for extended periods of time, likely in part due to the designing students having graduated and the extreme complexity of the project.
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====Industrial engines====
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{{Main|Industrial Engines}}
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Teams who are cost constrained, have cost as a team priority, or who have long-standing institutional knowledge/success with them may choose an engine not meant for traditional automotive use. Engines like these are similar to the Briggs engine used in FSAE Baja.
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==Engine control==
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{{Main|Engine Control}}
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Most modern engines are controlled by an engine control module (ECM) that determines when to inject the fuel and when to ignite the charge using various sensors and an engine tune. This electronic control strategy requires many sensors on the engine and a harness that interfaces with the ECM. These sensors come from the factory when purchasing an engine but can be changed to fit engine modifications or tuning requirements.
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The engine control is done through software, many off the shelf ECMs exist and come with their own software. Tuning a stock ECM is not recommended, it is much more difficult as it will require a software re-flash and OEMs do not make this easy. The ECM can also handle controls for accessory systems such as idle air control , turning cooling fans on and off, and some may be able to implement launch control.
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Most teams use alpha-n tuning due to it's simplicity of implementation.
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==Goals==
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The team's approach to the engine system is a balancing of multiple contradictory performance goals (power and torque, reliability, efficiency) as well as non-performance goals (cost, packaging, weight, serviceability, etc.). With all else being held constant, running an engine at a higher power level will sacrifice some reliability and often efficiency. The balance struck is a critical design choice taken by the team.
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===Reliability===
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Michael Royce in Learn & Compete states that “[reliability] must be the number one technical objective of the team”. Engine reliability can mean different things to different teams. To some it might mean that the engine finishes the endurance race. To other teams, one engine needs to last many years due to budget constraints. Because most engines are sourced from motorcycles that operate at higher power and higher speeds on the street than they do in FSAE, the operation of the engine may not play as big of a role in the engine's reliability as which engine is chosen, or how attentive the team is in servicing it. Failure of necessary, accessory systems such as [[Cooling|cooling]] or oiling will result in an engine failure, but that would not be the fault of the engine itself.
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====Engine choice====
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Engine to engine comparisons are difficult, and the literature is sparse at best. Most available engine specific reliability reports are anecdotal. However, brand comparisons are both easier and more widely available. Consumer Reports performed such a comprehensive study on motorcycle reliability<ref>https://www.consumerreports.org/cro/news/2015/04/who-makes-the-most-reliable-motorcycle/index.htm</ref>.
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The reliability study is focused on how often the bikes would need to have repairs within the first four years of purchase. The three big Japanese motorcycle companies, Yamaha, Suzuki, and Honda, are the only three with under 15% of the bikes with repairs needed. Yamaha leads the brands with 11% compared to the 12% for Honda and Suzuki each. It is important to consider that this study included the bike as a whole, and that for all of the studied motorcycles “mechanical engine problems were relatively rare, with only 3 percent having trouble with the cylinder head or valvetrain, or with the crankcase, crankshaft, or pistons. Similarly, only 3 percent needed transmission repairs, although 7 percent had clutch problems.” LA Times <ref>https://www.latimes.com/business/autos/la-fi-hy-consumer-reports-motorcycle-ratings-20160127-story.html</ref> researching this study reported an interview stating "European bikes are engineered for character and sex appeal, and Japanese bikes are engineered for reliability,". This sentiment can be found echoed in the FSAE online forums.
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When choosing an engine to purchase, consider its previous life. The engine's mileage and reason for being sold (was it in a crash?) may influence its lifetime in an FSAE car.
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====Servicing====
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Another aspect of reliability is parts and tools availability. The team should consider how easy is it to get hold of spare parts and/or special tools needed to service and fix the engine. The ubiquity of Japanese 4-cylinder engines increases the availability of parts, access to knowledge, and the likelihood that another team at the competition will have compatible parts in case your team has a critical failure.
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===Power & torque===
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All else being held equal, the car that produces more power will win the race. However, the primary function of the engine is to produce ''enough'' power to accomplish your designed team goals. Determining ''how much is enough'' is one of the fundamental questions to answer for the system. An overpowered engine may cause complications due to fuel consumption, packaging complexity, weight, etc.
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<!--There are a few ways to optimize engine power for your team goals. These include, but are not limited to:
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* Engine Choice
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* Engine Modifications
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* Spark and Fuel Tuning
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* Auxiliary System Tuning (Intake, exhaust, etc)
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I imagine there is a lot more to expand upon here - Novotny-->
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Recommended design questions to answer are: What performance goals drive torque and horsepower requirements? How much power and torque do we need to meet those performance goals? At what RPM should we make peak power? Torque? Answers to these questions depend heavily upon your team's design philosophy. Examples of teams design philosophy with regards to power and torque:
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* We have a novice driver - we want our torque curve to be wide and flat
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* We run a CVT and the engine will hold at a specific RPM during all events and we only want torque at that spot at the expense of all else
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* We are a first year team and we don't know what we are doing so we are just going for peak torque everywhere
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* We have the torque curve in the shape we want so we are just tuning for peak torque everywhere
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* We are running with huge boost and need to run with an AFR of 9 or else we'll be building a bomb
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* We can't get our engine to idle, so we're spending the whole year tuning at 1.5K RPM and didn't get around to anything else
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* Our driver is a 4th year masters student who has 8 years of FS driving and can put the engine wherever he wants, we are giving him peak torque at 9650 RPM because that's what gives him the fasted lap times during testing
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<!-- I dont think we need so many of these, but I'll leave them for now-->
  
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Torque and power ''must'' be experimentally determined by testing the engine on a dynamometer. Simulated and predicted engine performance will not reflect real world conditions.
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<!--(need page for dynos).-->
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====Restrictor====
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{{Main|Restrictor}}
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The air from the intake must pass through a small hole that sets a maximum theoretical power limit that FSAE cars can achieve. This performance cap promotes safety and facilitates a more level playing field.
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<!-- There used to be a section on a Piston Speed Limit, but I removed it - no such limitation exists in the FSAE rules (or the FS rules, as far as I can tell).
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There is a max test speed that is used for the Noise test, but this does not limit teams from exceeding that piston speed outside of the noise test.-->
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====Displacement limit====
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Contrary to popular belief, the displacement limit of 710ccs does ''not'' limit power. If a 6.2 liter V8 engine were allowed, it would not make more power than a regular FSAE four cylinder. This is because of the restrictor; a 6.2L engine would not be able to get enough air at a usable RPM range. The intent of the 710cc rule is to guide teams toward engines that work well with the restrictor.
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====Efficiency====
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{{Main|https://en.wikipedia.org/wiki/Engine_efficiency Engine Efficiency}}
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IC engines are quite inefficient, often 30% or lower. The excess energy goes into two main places: the exhaust and the cooling system. Energy can be extracted from the exhaust with a turbocharger (up until you reach the restrictor limit).
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<!--
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====Engine modifications====
  
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The purpose of an internal combustion engine is to convert the chemical energy in gasoline or ethanol into mechanical energy used to propel the car. The engine is one of the most complicated single parts of any vehicle.
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* To fill in, see note in editing for discussion points
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-->
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<!-- boring out cylinders, high compression pistons, porting intake or exhaust, lightening, removing stuff, custom parts, etc-->
  
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==Simulation==
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A common practice in introductory thermodynamics classes is to model the [[Otto Cycle|otto cycle]] in a program like Matlab. This practice can be expanded by further developing engine simulations, or by using a commercially available product.
  
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Ricardo WAVE or GT-Power are commonly used. At the 1D level, simulations are good for understanding trends, but not necessarily getting a precise power number. These trends can help identify what changes to the system will have positive or negative impacts and to what extent they will change the output. Specific problems arise in the 1D models for the highly 3D behavior air achieves through the restrictor and plenum. The strength really lies in getting an engineering understanding of how to design an intake and exhaust for a given torque curve e.g. runner length, exhaust collector strategy (4-2-1 or a 4-1 exhaust), and plenum size.
  
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An open source engine model made by Ange Yaghi (AngeTheGreat on youtube) is in early development and while developed to predict acoustic characteristics may be used or altered to simulate engine performance.
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==Oil System==
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{{Main|Oil}}
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The engine has to be constantly lubricated to continue designed function. All OEM engines come equipped with an internal oil system. Motorcycle engine oil systems need to be modified to be used in an FSAE context due to the lack of banking when turning. The oil to be used in the engine should be the specification used by the stock bike unless otherwise recommended by the manufacturer or an oil supplier. Using the wrong engine oil may reduce the lifetime of the engine by an unknown amount as well as decrease performance.
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==Mounting and installation==
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The mounting of the engine should follow the manufacturer recommendations for bolts, torque, and vibration isolation. In the case of larger, usually 4 cylinder, engines, it is important to consider installation and removal when designing the frame mounting. Most teams install the engine from above, allowing the car to rest on the ground, or its wheels, and a small engine hoist can be conscripted to lift and hold the engine into the correct place in the car. Some teams load the engine from below, using the cars reduced weight sans engine to their advantage. Each method of engine installation requires a large opening to be left that may reduce the frame stiffness, roll hoop bracing, or force other packaging compromises.
  
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Current/proposed outline:
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Another design solution is to utilize a rear subframe. Subframes are seen on hybrid monocoque cars, but are also implemented in some tube frame chassis. Subframes are often employed to hold the differential, jacking bar, rear aero package and even sometimes part or all of the rear suspension. Having a subframe allows the engine to be installed without an engine sized hole in the frame.
  
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It is rare to see implemented but the rules explicitly allow removable main roll hoop braces in F.5.12. This can be utilized to aid in engine installation similarly to a subframe by allowing the frame to close around the engine once installed.
  
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Engine
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==Best practices==
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* Basic ICE theory
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Engines can be incredibly robust to a wide variety of working conditions as long as they have air, compression, fuel, spark, and oil. That being said, there are many places where a little love and care will reap huge benefits.
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* structure of typical engine
 
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* Goals for engine in FS context -reliability, efficiency, power
 
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* Common engines
 
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* Best Practices
 
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* rant about wankels not being allowed
 
  
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=Theory=
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Many of the systems inside the engine operate on small tolerances. These tolerances mean it's wise to care for your engine, if you want it to last. Often, you can operate an engine outside of many of these tolerances, but you will lose performance and often risk severe damage to the components if not catastrophic failure.
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Thermo - stick to the basics, there's enough thermo explanations in the world as is i think. I've just copy/pasted this from my old documentation, so it's written pretty informally.
 
  
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When purchasing an engine, it is good practice to tear it down and inspect all parts for tolerance. If the engine is used, this is exponentially more important, as you will need to check for wear as well. Many teams (in the US) purchase used engines from motorcycle crashes, which can cause subtle damage to the internals, even if none is present on the outside of the engine.
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===Servicing===
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Servicing an engine can be as simple as changing the oil and as in depth as changing main bearings. It will be well worth the investment to buy a service manual for the engine, or find a pdf online to print, and put together in a binder. If putting the pages in a binder, using plastic sleeves will protect the pages from oil damage. If using a book... be careful.
  
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If the team is buying a used engine, perform a full engine teardown and service to ensure the engine is in full working condition.
  
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'''Teardown/Rebuild'''
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* Valvetrain
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** Take the chance to measure your cams if you can for accurate simulations.
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** Correct lashing
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** Valve seating
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* Head <!--lol-->
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** check flatness, possibly deck
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* Block
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** Clean surface
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** Check flatness, possibly deck
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** Check cylinder roundness, if too far out of spec you'll lose a significant amount of power.
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** Hone cylinders if changing rings, or if too shiny
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* Pistons
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** Clean faces
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** Check rod bearings for wear
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** Check rings, likely good idea to replace if any blow-by on piston
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* Crankcase
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** Check for metal bits lol
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* Get a new set of gaskets (MLS head gasket can likely be reused depending on condition)
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* Get a new set of all TTY bolts
  
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A typical gasoline engine has four strokes:(1) Induction, (2) Compression, (3) Combustion, and (4) Exhaust.
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====Routine maintenance====
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The service schedule of an engine used in FSAE is highly dependent on the team. While more frequent service is almost always better, the fact that the mechanics are potentially inexperienced students in a dirty environment, each time the engine is opened, there is a chance that contaminants will be introduced or that the engine will be re-assembled incorrectly. A good guideline is to service the engine as directed by the manufacturer.
  
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====How to diagnose issues====
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Engines will slowly wear in and wear out over time. The easiest issue to diagnose is a hole in the block. Most issues are not as simple to spot. Auditory cues, loss of power (sudden or gradual) and trouble cranking or shifting can indicate engine trouble.
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==Common engines and modifications==
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<!-- I think bc the cbr, r6, and a few of the 450s are so common, we can use this to list what we have done to optimize for FSAE use.
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Example: gear removal, EWP, custom valving, suggested idles, mounting tips, weights/mass, stock water pump flow rates, oil recommendations, intake mounting recs. exhaust mounting recs, heat generation, wiring, injectors
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-->
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===Honda CBR600RR===
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* Many teams remove first gear which has a very high gear ratio and has a large gap to second gear, limiting its usability.
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* The engine will need a max heat dissipation of about 10kW from cooling system <ref>U Toronto 2007 https://manualzz.com/doc/35576578/design-and-optimzation-of-a-formula-sae-cooling</ref>
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* Some teams remove the thermostat control to keep temps down by forcing coolant circulation through the radiator at all times. This is not a universally accepted modification, albeit one of low stakes. The disagreeing viewpoint is that the thermal mass of the engine and cooling circuit is high enough that you won't get into trouble running the OEM thermostat if the cooling system operates correctly, and the engine is happier when it is at temperature. This is a relatively minor modification so running a lap with and without could be a decent test, and there is almost no risk to the vehicle.
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* Some teams run Yamaha R6 oil filter because it is one inch shorter and attached to a different point on the engine <ref>https://www.reddit.com/r/FSAE/comments/11ljx6f/2008_cbr600rr_low_profile_oil_filter/</ref>
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===Yamaha R6===
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* If you have used an R6, please help us by adding what you/your team has done to optimize the engine for FSAE use.
  
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<br /> Strokes (4) and (1) are used to exchange the burned fuel air mixture from each stroke and replace it with clean fresh air from outside respectively. Stroke (2) is used to increase the density of the charge, greatly improving the amount of work that can be obtained from each unit of fuel. Stroke (3) is the result of the detonation and explosion of the charge forcing the combustion chamber to expand, converting the chemical energy of the gasoline to mechanical work.When each stroke is plotted on a chart comparing pressure and volume of the combustion chamber, the cycle analysis becomes easier.
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===Yamaha WR/YZ450===
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* WPI runs WiSECO high compression piston
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* Be cognizant of the different generations of WR/YZ450F when buying engines and parts. Pre-2016 engines are 5 valve heads with the exhaust port on the front of the head, 2016+ are 4 valve with the exhaust port on the rear.
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* Stock engine does not have bungs/take-offs for oil temperature or pressure. The filter cap is a convenient place to add a bung, as is the oil pressure check port.
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* Oil pressure is often low compared to a street bike engine (CBR600RR, R6, etc.). Most of the engine bearings are roller bearings, so oil pressure will tend to be lower. 10-20 psi at idle and ~4-5 psi(both measured from the filter cap) under lateral acceleration seems to be common.
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* Stock engine does not have a cam position sensor, however there is space on the valve cover to add one.
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* 1st gear will likely be unusable for launching, depending on final drive. Consider the gearset from the other engine (ie: if you have a WR, look at a YZ gearset. If you have a YZ, look at a WR gearset).
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* Many parts are common between the WR and YZ, with the main exceptions being the transmission gearset and the cams.
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* Stock mechanical water pump will likely not provide enough mass flow for adequate heat rejection.
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* Oil temperature may be difficult to manage. The WR/YZ450 engine family does not have an oil to water heat exchanger, heat rejection from the oil is through heat transfer into adjacent water passages.
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* Starter geartrain seems to be strong enough for higher cranking loads seen in FSAE use (we ran a used engine with unknown history for a year and didn't have any issues with the starter geartrain breaking knock on wood).
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* 2016 WR450F weighed 30.45 kg without oil or coolant. Oil was 0.61 kg and a stock engine sprocket was 0.09 kg.
 +
* Further reading:
 +
** [https://drive.google.com/file/d/1Q5XaHZGjjahw5Ws1lvxdjKbLsm6vQtQK/view?usp=sharing UWaterloo Formula Motorsports - WR450F Engine Project  (1/3)]<br />
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** [https://drive.google.com/file/d/1U0y8geJOM3BxuCZlj71QGqXQ9cna6RCr/view?usp=sharing UWaterloo Formula Motorsports - WR450F Engine Project (3/3)]
  
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==Notable history of FSAE engines==
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pulled from fsaeonline.com <ref>https://www.fsaeonline.com/page.aspx?pageid=c4c5195a-60c0-46aa-acbf-2958ef545b72</ref>
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* SAE Mini Indy with B&S Engine - 1980
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* New FSAE comp set up with any 4-stroke engine allowed incl. wankel and diesel
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** intake restriction at 1 inch
  
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[insert pv diagram]
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1983 - Marquette University ran the first turbo
  
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Strokes (4) and (1) perform the gas exchange process, allowing the engine to “breathe”. In a simplified case, the engine inducts and exhausts to atmospheric pressure. This is called pump work, but is negligible for the model used here. The difference in the work done by the engine to compress the charge and the work done by the exploding charge on the piston, strokes (2) and (3), is the engine work. From this analysis, we have two simple ways to characterize an engine: how much work we get each cycle, and how much we have to pay for the work we get, or the cycle’s efficiency. ''The sum of the work for the entire cycle can be visualized as the area circled by the cycle on the PV diagram. This is called the net cycle work. Because it is the net cycle work found in a simplified, ideal case, we call it the ideal net work or otto cycle net work.The efficiency of the cycle is more difficult to visualize as it is a ratio of the work produced by the engine to the chemical energy supplied. From the PV diagram, this can be the ratio of the area inside the curve to the line segment 23, or the difference in the lengths of line segments 23 and 41. However, these visualizations are non-intuitive and can be better expressed numerically.However, this simplified model won’t hold much water when we need to improve engine performance.''There are a few key things glossed over for ease of theoretical calculations that play a significant role in the operation of the engine. The first, and largest factor in differentiating real engine performance from theoretical is that all of the processes in the cycle take time. The key example of this is the combustion of the charge in a real engine is not instantaneous and occurs over a drawn out period of time. This removes the sharp peak on the PV diagram. Our limited power over the physics of flame propagation speed will put this factor far beyond the scope of this section and we will not discuss it’s finer points here.
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1984 - rules allowed nitrous oxide
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Another key characteristic of real engine performance is cylinder pressure during gas exchange processes. To induce induction into the combustion chamber, the pressure inside must be lower than the pressure of the atmosphere. Similarly, the exhaust pressure inside the cylinder must be higher than atmospheric or else the charge would not exit the cylinder. Thus, the work done by the air on the engine during induction is less than the work done on the engine to the exhaust charge. This work done to facilitate the gas exchange process is known as pump work. Because the intake charge is at a lower pressure and thus less dense than the theoretical maximum of atmospheric air, this allows us to analyze the performance of the engine based on how much air it actually breathes in versus the theoretical maximum. This is known as volumetric efficiency. The lower the manifold, or cylinder, pressure is, the lower its volumetric efficiency. Special tricks can be played with manifold tuning and resonances to increase engine performance or even temporarily achieve greater than 100% volumetric efficiency. One trick that is particularly important in high revving engines is scavenging. Scavenging is the harnessing of exhaust manifold kinetic energy to help draw additional clean air into the cylinder or using similarly using intake air energy to aid in the removal of low energy exhaust gasses. This is achieved by elegant cylinder head and port geometry, but also camshaft timing. If the intake and exhaust valves are open simultaneously, the scavenging effect can be further tuned. This is known as valve-overlap. For high engine speeds, the volumetric efficiency plummets as it is much more difficult to fill the cylinder adequately, so greater valve overlap is used to compensate. Another factor that is seen in real engine performance is what happens when the engine is not allowed to breathe as much as it wants. This is known as throttling. This is done to modulate speed when driving, as one opens and closes the throttle. Throttling is an isenthalpic process that drops the pressure and temperature of a gas at the expense of increase entropy, turbulence and/or friction against the throttle body. This pressure drop has three large effects. One, the volumetric efficiency plummets. Two, the pump work of each cycle increases. Three, less power can be drawn from the engine.
 
  
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=Structure=
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1985 - UT Austin ran an in-house-designed supercharger on a 300cc Wankel
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I think wikipedia does a very detailed explanation on general engine layout, i think we should probably focus on bike engines w.r.t. fsae competitions.
 
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=Goals=
 
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Not sure if we should be saying what is or isn't more important than something else, i think thats up to the teams, so in no particular order:
 
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==Reliability==
 
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engine no go boom
 
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==Power==
 
−
gasoline go boom
 
−
==Efficiency==
 
−
high speed low drag babey
 
−
=Best Practices=
 
−
How to care for an engine.
 
  
 +
1988 - e85 class established
  
−
How/when to service.
+
1989 - Kawasaki 600cc Ninja ~50% of all cars
  
 +
1995 - Honda CBR600 ~50% of all cars
  
−
How to diagnose issues.
+
2001 - WWU ran a custom 554cc V8<ref>https://wwuracing.com/our_cars#V30</ref>
  
 +
2003 - Kansas State did the first "sidewinder" (engine on side)
  
−
Why combustion is more romantic than electric.
+
2004 - Guelph ran the first IC AWD in FSAE (not sure about in FS, uas graz may have them beat by a year| Newcastle may have done it in 2003 at FSAE-A) (not sure if it beat the EV AWDs)
−
=Common Engines=
 
−
I think bc the cbr, r6, and a few of the 450s are so common, we can use this to list what we have done to optimize for FSAE use.
 
  
 +
2005 - Cornell ran 5 fuel injectors, the 5th going into the turbo (?)
  
−
Example: gear removal, EWP, custom valving, suggested idles, mounting tips, weights/mass, stock water pump flow rates, oil recomendations, intake mounting recs. exhaust mounting recs, heat generation, wiring, injectors
+
2017 - FSAE rules change from 610cc to 710cc maximum displacement
 +
==References==
 +
[[Category: Internal Combustion]]

Latest revision as of 00:53, 6 June 2023

The engine is the center of the internal combustion powertrain system. All other components of the greater system exist to service the engine in different ways. This means the engine is sensitive to design changes made across the entire powertrain. As of 2022, the FSAE rules require an internal combustion engine with a displacement of 710cc or less[1]. Available OEM motors within this displacement limit are largely sourced from motorcycles and snowmobiles. The purpose of the engine is to convert the chemical energy in gasoline or ethanol into mechanical energy used to propel the car. The engine is one of the most complicated and often heaviest single parts of any vehicle.

System design and engine choice

Main page: List of Engines

When designing the engine subsystem, the critical choice is to buy an engine or build a custom solution. Due to their complexity, both in design and manufacturing, most teams purchase an engine off the shelf. Once an engine has been selected, the engine itself will require a suite of accessory systems to run. "Engine tuning" is almost always referring to the tuning of these accessory systems such as fuel and spark timing. However, even if buying an engine, many options are available to teams to customize or modify the engine in order to optimize performance for team goals.

Wikipedia does a very detailed explanation on general engine layout so that will not be covered here.

The competition limits engine choice to a four-stroke, piston engine. The four strokes (intake, compression, power, exhaust) can be remembered by the crass pneumonic "suck, squeeze, bang, blow". Rotary engines have competed in the past but were banned due to difficulty legislating displacement restrictions compared to a conventional piston engine. Most of the engines used in FS/FSAE are adapted from small personal vehicles such as motorcycles and snowmobiles.

Motorcycle engines

Motorcycle engines make up the vast majority of engines used in FS/FSAE. The structure and operation of motorcycle engines differ from typical car engines in a few key places such as size, layout, and red line, etc. The two most common bike engine types used are

  1. 600cc 4 cylinders weighing between 100-150 lbs (45-70kg) and producing about 125-140hp stock
  2. Single cylinder 450cc engines typically that weigh in the neighborhood of 70-90 pounds (30-40kg)

These engines are almost exclusively overhead cam layout.

Four cylinder engines

These bike engines are supersport engines and already configured to power a motorcycle in the same weight range as most FS/FSAE cars at a high level. These are easily adapted to use in a FSAE vehicle with modifications to the ancillary systems. The reliability and lower cost of these engines make them the most common choice in modern FSAE competitions. A 4 cylinder design smooths air flow through the restrictor as well as power delivery to the drive sprocket. The higher number of cylinders drives a more complicated intake and exhaust design. Additionally, the larger size and greater weight means packaging the engines may be more difficult than a smaller engine. The complexity of the engine internals may be a hurdle for servicing and in turn may drive rebuild issues if not done carefully. 4 cylinder engines in competition frequently see power figures in the 60-80hp range. Because of their higher power, cars that run these engines usually have a higher power to weight ratio than cars that run a single cylinder engine, despite the weight increase. These engines are also quite cheap, since you can buy engines from crashed bikes for not a lot of money (and usually the only thing damaged is the side covers).

Three cylinder engines

This category exists mostly because of Triumph's 675cc Daytona and Street Triple engines. They can provide similar power with less complexity than the four cylinder engines. They also have a higher displacement than any of the four cylinder engines.

Two cylinder engines

While rarer, some teams run two cylinder engines. Both V-twin and parallel twin engines exist in FSAE sizes. They generally lie somewhere between singles and four cylinders in terms of pros and cons. They may not make the same amount of power as the four cylinder engines but they are smoother than the single cylinder engines and less complex than the four cylinder engines.

Single cylinder engines

Single cylinder engines generally come from bikes built for motocross or on a motocross platform such as the Yamaha YZ450. These engines are lighter, and their reduced size makes packaging the engine and the ancillary systems much easier. The size and low weight of these engines allow them to be carried by a person without too much difficulty, easing transportation.

The single cylinder results in a more dramatic pulsed flow through the intake restrictor making it more difficult for these engines to reach the high hp figures reached by a 4 cylinder engine. However the simplicity of the engine, intake, and exhaust system makes these engines a prime target for turbocharging which not only smooths out the pulsed flow, but also allows these to reach power figures in the same range as a naturally aspirated 4 cylinder or higher.

Some designs such as the Yamaha YZ450F have the intake port in the front and the exhaust port in the back making exhaust routing even easier as it does not need to pass between the engine and the driver[2].

Snowmobile engines

If you have used a snowmobile engine, please help us by adding what you/your team has done to implement the engine in an FSAE context.

Other engines

Beyond the motorcycle and snowmobile engines, some teams go to more exotic design solutions, some even designing or using a custom engine.

Custom engines

Driven by either extreme performance goals, or academic pursuit, there is a history of custom FSAE engines. Most of these use or adapt internals from a motorcycle engine such as the pistons, or crankshaft, within a custom billet crankcase. However, with industry involvement, such as in the case of the Mahle or AMG engines, an entirely custom design can be utilized. Few of the custom engines remain in use for extended periods of time, likely in part due to the designing students having graduated and the extreme complexity of the project.

Industrial engines

Main page: Industrial Engines

Teams who are cost constrained, have cost as a team priority, or who have long-standing institutional knowledge/success with them may choose an engine not meant for traditional automotive use. Engines like these are similar to the Briggs engine used in FSAE Baja.

Engine control

Main page: Engine Control

Most modern engines are controlled by an engine control module (ECM) that determines when to inject the fuel and when to ignite the charge using various sensors and an engine tune. This electronic control strategy requires many sensors on the engine and a harness that interfaces with the ECM. These sensors come from the factory when purchasing an engine but can be changed to fit engine modifications or tuning requirements.

The engine control is done through software, many off the shelf ECMs exist and come with their own software. Tuning a stock ECM is not recommended, it is much more difficult as it will require a software re-flash and OEMs do not make this easy. The ECM can also handle controls for accessory systems such as idle air control , turning cooling fans on and off, and some may be able to implement launch control.

Most teams use alpha-n tuning due to it's simplicity of implementation.

Goals

The team's approach to the engine system is a balancing of multiple contradictory performance goals (power and torque, reliability, efficiency) as well as non-performance goals (cost, packaging, weight, serviceability, etc.). With all else being held constant, running an engine at a higher power level will sacrifice some reliability and often efficiency. The balance struck is a critical design choice taken by the team.

Reliability

Michael Royce in Learn & Compete states that “[reliability] must be the number one technical objective of the team”. Engine reliability can mean different things to different teams. To some it might mean that the engine finishes the endurance race. To other teams, one engine needs to last many years due to budget constraints. Because most engines are sourced from motorcycles that operate at higher power and higher speeds on the street than they do in FSAE, the operation of the engine may not play as big of a role in the engine's reliability as which engine is chosen, or how attentive the team is in servicing it. Failure of necessary, accessory systems such as cooling or oiling will result in an engine failure, but that would not be the fault of the engine itself.

Engine choice

Engine to engine comparisons are difficult, and the literature is sparse at best. Most available engine specific reliability reports are anecdotal. However, brand comparisons are both easier and more widely available. Consumer Reports performed such a comprehensive study on motorcycle reliability[3].

The reliability study is focused on how often the bikes would need to have repairs within the first four years of purchase. The three big Japanese motorcycle companies, Yamaha, Suzuki, and Honda, are the only three with under 15% of the bikes with repairs needed. Yamaha leads the brands with 11% compared to the 12% for Honda and Suzuki each. It is important to consider that this study included the bike as a whole, and that for all of the studied motorcycles “mechanical engine problems were relatively rare, with only 3 percent having trouble with the cylinder head or valvetrain, or with the crankcase, crankshaft, or pistons. Similarly, only 3 percent needed transmission repairs, although 7 percent had clutch problems.” LA Times [4] researching this study reported an interview stating "European bikes are engineered for character and sex appeal, and Japanese bikes are engineered for reliability,". This sentiment can be found echoed in the FSAE online forums.

When choosing an engine to purchase, consider its previous life. The engine's mileage and reason for being sold (was it in a crash?) may influence its lifetime in an FSAE car.

Servicing

Another aspect of reliability is parts and tools availability. The team should consider how easy is it to get hold of spare parts and/or special tools needed to service and fix the engine. The ubiquity of Japanese 4-cylinder engines increases the availability of parts, access to knowledge, and the likelihood that another team at the competition will have compatible parts in case your team has a critical failure.

Power & torque

All else being held equal, the car that produces more power will win the race. However, the primary function of the engine is to produce enough power to accomplish your designed team goals. Determining how much is enough is one of the fundamental questions to answer for the system. An overpowered engine may cause complications due to fuel consumption, packaging complexity, weight, etc.

Recommended design questions to answer are: What performance goals drive torque and horsepower requirements? How much power and torque do we need to meet those performance goals? At what RPM should we make peak power? Torque? Answers to these questions depend heavily upon your team's design philosophy. Examples of teams design philosophy with regards to power and torque:

  • We have a novice driver - we want our torque curve to be wide and flat
  • We run a CVT and the engine will hold at a specific RPM during all events and we only want torque at that spot at the expense of all else
  • We are a first year team and we don't know what we are doing so we are just going for peak torque everywhere
  • We have the torque curve in the shape we want so we are just tuning for peak torque everywhere
  • We are running with huge boost and need to run with an AFR of 9 or else we'll be building a bomb
  • We can't get our engine to idle, so we're spending the whole year tuning at 1.5K RPM and didn't get around to anything else
  • Our driver is a 4th year masters student who has 8 years of FS driving and can put the engine wherever he wants, we are giving him peak torque at 9650 RPM because that's what gives him the fasted lap times during testing

Torque and power must be experimentally determined by testing the engine on a dynamometer. Simulated and predicted engine performance will not reflect real world conditions.

Restrictor

Main page: Restrictor

The air from the intake must pass through a small hole that sets a maximum theoretical power limit that FSAE cars can achieve. This performance cap promotes safety and facilitates a more level playing field.

Displacement limit

Contrary to popular belief, the displacement limit of 710ccs does not limit power. If a 6.2 liter V8 engine were allowed, it would not make more power than a regular FSAE four cylinder. This is because of the restrictor; a 6.2L engine would not be able to get enough air at a usable RPM range. The intent of the 710cc rule is to guide teams toward engines that work well with the restrictor.

Efficiency

Main page: [Engine Efficiency]

IC engines are quite inefficient, often 30% or lower. The excess energy goes into two main places: the exhaust and the cooling system. Energy can be extracted from the exhaust with a turbocharger (up until you reach the restrictor limit).

Simulation

A common practice in introductory thermodynamics classes is to model the otto cycle in a program like Matlab. This practice can be expanded by further developing engine simulations, or by using a commercially available product.

Ricardo WAVE or GT-Power are commonly used. At the 1D level, simulations are good for understanding trends, but not necessarily getting a precise power number. These trends can help identify what changes to the system will have positive or negative impacts and to what extent they will change the output. Specific problems arise in the 1D models for the highly 3D behavior air achieves through the restrictor and plenum. The strength really lies in getting an engineering understanding of how to design an intake and exhaust for a given torque curve e.g. runner length, exhaust collector strategy (4-2-1 or a 4-1 exhaust), and plenum size.

An open source engine model made by Ange Yaghi (AngeTheGreat on youtube) is in early development and while developed to predict acoustic characteristics may be used or altered to simulate engine performance.

Oil System

Main page: Oil

The engine has to be constantly lubricated to continue designed function. All OEM engines come equipped with an internal oil system. Motorcycle engine oil systems need to be modified to be used in an FSAE context due to the lack of banking when turning. The oil to be used in the engine should be the specification used by the stock bike unless otherwise recommended by the manufacturer or an oil supplier. Using the wrong engine oil may reduce the lifetime of the engine by an unknown amount as well as decrease performance.

Mounting and installation

The mounting of the engine should follow the manufacturer recommendations for bolts, torque, and vibration isolation. In the case of larger, usually 4 cylinder, engines, it is important to consider installation and removal when designing the frame mounting. Most teams install the engine from above, allowing the car to rest on the ground, or its wheels, and a small engine hoist can be conscripted to lift and hold the engine into the correct place in the car. Some teams load the engine from below, using the cars reduced weight sans engine to their advantage. Each method of engine installation requires a large opening to be left that may reduce the frame stiffness, roll hoop bracing, or force other packaging compromises.

Another design solution is to utilize a rear subframe. Subframes are seen on hybrid monocoque cars, but are also implemented in some tube frame chassis. Subframes are often employed to hold the differential, jacking bar, rear aero package and even sometimes part or all of the rear suspension. Having a subframe allows the engine to be installed without an engine sized hole in the frame.

It is rare to see implemented but the rules explicitly allow removable main roll hoop braces in F.5.12. This can be utilized to aid in engine installation similarly to a subframe by allowing the frame to close around the engine once installed.

Best practices

Engines can be incredibly robust to a wide variety of working conditions as long as they have air, compression, fuel, spark, and oil. That being said, there are many places where a little love and care will reap huge benefits.

Many of the systems inside the engine operate on small tolerances. These tolerances mean it's wise to care for your engine, if you want it to last. Often, you can operate an engine outside of many of these tolerances, but you will lose performance and often risk severe damage to the components if not catastrophic failure.

When purchasing an engine, it is good practice to tear it down and inspect all parts for tolerance. If the engine is used, this is exponentially more important, as you will need to check for wear as well. Many teams (in the US) purchase used engines from motorcycle crashes, which can cause subtle damage to the internals, even if none is present on the outside of the engine.

Servicing

Servicing an engine can be as simple as changing the oil and as in depth as changing main bearings. It will be well worth the investment to buy a service manual for the engine, or find a pdf online to print, and put together in a binder. If putting the pages in a binder, using plastic sleeves will protect the pages from oil damage. If using a book... be careful.

If the team is buying a used engine, perform a full engine teardown and service to ensure the engine is in full working condition.

Teardown/Rebuild

  • Valvetrain
    • Take the chance to measure your cams if you can for accurate simulations.
    • Correct lashing
    • Valve seating
  • Head
    • check flatness, possibly deck
  • Block
    • Clean surface
    • Check flatness, possibly deck
    • Check cylinder roundness, if too far out of spec you'll lose a significant amount of power.
    • Hone cylinders if changing rings, or if too shiny
  • Pistons
    • Clean faces
    • Check rod bearings for wear
    • Check rings, likely good idea to replace if any blow-by on piston
  • Crankcase
    • Check for metal bits lol
  • Get a new set of gaskets (MLS head gasket can likely be reused depending on condition)
  • Get a new set of all TTY bolts

Routine maintenance

The service schedule of an engine used in FSAE is highly dependent on the team. While more frequent service is almost always better, the fact that the mechanics are potentially inexperienced students in a dirty environment, each time the engine is opened, there is a chance that contaminants will be introduced or that the engine will be re-assembled incorrectly. A good guideline is to service the engine as directed by the manufacturer.

How to diagnose issues

Engines will slowly wear in and wear out over time. The easiest issue to diagnose is a hole in the block. Most issues are not as simple to spot. Auditory cues, loss of power (sudden or gradual) and trouble cranking or shifting can indicate engine trouble.

Common engines and modifications

Honda CBR600RR

  • Many teams remove first gear which has a very high gear ratio and has a large gap to second gear, limiting its usability.
  • The engine will need a max heat dissipation of about 10kW from cooling system [5]
  • Some teams remove the thermostat control to keep temps down by forcing coolant circulation through the radiator at all times. This is not a universally accepted modification, albeit one of low stakes. The disagreeing viewpoint is that the thermal mass of the engine and cooling circuit is high enough that you won't get into trouble running the OEM thermostat if the cooling system operates correctly, and the engine is happier when it is at temperature. This is a relatively minor modification so running a lap with and without could be a decent test, and there is almost no risk to the vehicle.
  • Some teams run Yamaha R6 oil filter because it is one inch shorter and attached to a different point on the engine [6]

Yamaha R6

  • If you have used an R6, please help us by adding what you/your team has done to optimize the engine for FSAE use.

Yamaha WR/YZ450

  • WPI runs WiSECO high compression piston
  • Be cognizant of the different generations of WR/YZ450F when buying engines and parts. Pre-2016 engines are 5 valve heads with the exhaust port on the front of the head, 2016+ are 4 valve with the exhaust port on the rear.
  • Stock engine does not have bungs/take-offs for oil temperature or pressure. The filter cap is a convenient place to add a bung, as is the oil pressure check port.
  • Oil pressure is often low compared to a street bike engine (CBR600RR, R6, etc.). Most of the engine bearings are roller bearings, so oil pressure will tend to be lower. 10-20 psi at idle and ~4-5 psi(both measured from the filter cap) under lateral acceleration seems to be common.
  • Stock engine does not have a cam position sensor, however there is space on the valve cover to add one.
  • 1st gear will likely be unusable for launching, depending on final drive. Consider the gearset from the other engine (ie: if you have a WR, look at a YZ gearset. If you have a YZ, look at a WR gearset).
  • Many parts are common between the WR and YZ, with the main exceptions being the transmission gearset and the cams.
  • Stock mechanical water pump will likely not provide enough mass flow for adequate heat rejection.
  • Oil temperature may be difficult to manage. The WR/YZ450 engine family does not have an oil to water heat exchanger, heat rejection from the oil is through heat transfer into adjacent water passages.
  • Starter geartrain seems to be strong enough for higher cranking loads seen in FSAE use (we ran a used engine with unknown history for a year and didn't have any issues with the starter geartrain breaking knock on wood).
  • 2016 WR450F weighed 30.45 kg without oil or coolant. Oil was 0.61 kg and a stock engine sprocket was 0.09 kg.
  • Further reading:

Notable history of FSAE engines

pulled from fsaeonline.com [7]

  • SAE Mini Indy with B&S Engine - 1980
  • New FSAE comp set up with any 4-stroke engine allowed incl. wankel and diesel
    • intake restriction at 1 inch

1983 - Marquette University ran the first turbo

1984 - rules allowed nitrous oxide

1985 - UT Austin ran an in-house-designed supercharger on a 300cc Wankel

1988 - e85 class established

1989 - Kawasaki 600cc Ninja ~50% of all cars

1995 - Honda CBR600 ~50% of all cars

2001 - WWU ran a custom 554cc V8[8]

2003 - Kansas State did the first "sidewinder" (engine on side)

2004 - Guelph ran the first IC AWD in FSAE (not sure about in FS, uas graz may have them beat by a year| Newcastle may have done it in 2003 at FSAE-A) (not sure if it beat the EV AWDs)

2005 - Cornell ran 5 fuel injectors, the 5th going into the turbo (?)

2017 - FSAE rules change from 610cc to 710cc maximum displacement

References

  1. ↑ 2022 fsae rules PDF: https://www.fsaeonline.com/cdsweb/gen/DownloadDocument.aspx?DocumentID=25e8885c-7397-4b2d-93b3-fc404960bab1
  2. ↑ https://www.wheelsinmotionmc.com/inventory/v1/Current/Yamaha/Motorcycle/Cross-Country/WR450F/Base--Chatsworth-California---19488751?format=print
  3. ↑ https://www.consumerreports.org/cro/news/2015/04/who-makes-the-most-reliable-motorcycle/index.htm
  4. ↑ https://www.latimes.com/business/autos/la-fi-hy-consumer-reports-motorcycle-ratings-20160127-story.html
  5. ↑ U Toronto 2007 https://manualzz.com/doc/35576578/design-and-optimzation-of-a-formula-sae-cooling
  6. ↑ https://www.reddit.com/r/FSAE/comments/11ljx6f/2008_cbr600rr_low_profile_oil_filter/
  7. ↑ https://www.fsaeonline.com/page.aspx?pageid=c4c5195a-60c0-46aa-acbf-2958ef545b72
  8. ↑ https://wwuracing.com/our_cars#V30
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