Difference between revisions of "Engine"
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==Power & Torque== | ==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. | + | 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. There are a few ways to optimize engine power for your team goals. These include, but are not limited to: |
| + | |||
* Engine Choice | * Engine Choice | ||
* Engine Modifications | * Engine Modifications | ||
* Spark and Fuel Tuning | * Spark and Fuel Tuning | ||
* Auxiliary System Tuning (Intake, exhaust, etc) | * Auxiliary System Tuning (Intake, exhaust, etc) | ||
| − | I imagine there is a lot more to expand upon here - Novotny | + | <!--I imagine there is a lot more to expand upon here - Novotny--> |
| + | |||
| + | Recommended design questions to answer are: At what RPM should we make peak power? Torque? To all of these questions, it depends heavily upon your team's design philosophy. All could be approximated from a rudimentary lap-time simulation, but will need to be confirmed via testing. | ||
Examples of teams design philosophy: | Examples of teams design philosophy: | ||
| Line 71: | Line 74: | ||
* 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 thats what gives him the fasted lap times during testing | * 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 thats what gives him the fasted lap times during testing | ||
| − | Torque and power are determined by testing the engine on a dynomometer (need page for dynos). | + | Torque and power are determined by testing the engine on a dynomometer. |
| + | <!--(need page for dynos).--> | ||
| + | |||
==Power Limiting Factors== | ==Power Limiting Factors== | ||
====Restrictor==== | ====Restrictor==== | ||
Revision as of 12:00, 26 January 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.
Contents
System Design
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.
Engine Choice
- Main page: List of Engines
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". 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
- 600cc 4 cylinders weighing between 100-150 lbs (45-70kg) and producing about 125-140hp stock
- 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.
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 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 single cylinder engines 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
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. 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.
Goals
The team's approach to the engine system is a balancing of multiple contradictory goals. 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.
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.
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.
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. There are a few ways to optimize engine power for your team goals. These include, but are not limited to:
- Engine Choice
- Engine Modifications
- Spark and Fuel Tuning
- Auxiliary System Tuning (Intake, exhaust, etc)
Recommended design questions to answer are: At what RPM should we make peak power? Torque? To all of these questions, it depends heavily upon your team's design philosophy. All could be approximated from a rudimentary lap-time simulation, but will need to be confirmed via testing.
Examples of teams design philosophy:
- 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 dont 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 thats what gives him the fasted lap times during testing
Torque and power are determined by testing the engine on a dynomometer.
Power Limiting Factors
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.
Piston Speed Limit
The competition limits the engine speeds allowed[5].
a. Automotive / Motorcycle engines 914.4 m/min (3,000 ft/min) b. Industrial Engines 731.5 m/min (2,400 ft/min) The calculated speed will be rounded to the nearest 500 rpm.
A Honda CBR600RR has a stroke of 42.5mm or 0.0425 m. The piston traverses the stroke length twice during one revolution of the engine. This yields 0.085m/revolution. A max piston speed of 914.4 m/min allows a max RPM of about 10,757 RPM. This is usually rounded to 11,000 RPM. (Max piston speed is much more complicated than what is used here, but the actual variation is not significant enough to change the way the system is designed)
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. This may be modified for specific use in FSAE.
Best Practices
Engines can be incredibly robust to 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 CBR 600RR
- remove first gear, breaks traction with any reasonable FDR
- max heat dissipation of ~10kW needed from cooling system (utoronto 2007[6])
- remove the thermostat control to keep temps down (this is something I am skeptical of. 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)
Yamaha R6
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.
see all engines here
See Also
- UWaterloo Formula Motorsports - WR450F Engine Project (1/3)
- UWaterloo Formula Motorsports - WR450F Engine Project (3/3)
