Intake

Topics to add:

packaging

material choice

heat management

heating from restrictor

Current/Proposed Outline:

Basic theory

Intake system diagram

The intake system's purpose is to direct ambient air to your engine's air intake. On more traditional road cars and unrestricted race cars, the throttle is generally placed at the inlet of your intake runner (probably should have a source) to promote fast engine response. However, allowing a manifold between the restrictor and throttle body will limit the effects of the restriction(citation). This is negated in FSAE by preventing a large volume (plenum/manifold, intercooler, etc.) prior to the throttle body. The order of system components defined by rules can be seen in the figure right and each component is discussed further down this page.

Throttle control

should probably move down - not important enough to be all the way up here. The throttle allows modulation of the air coming into your intake system. Within FSAE, the throttle must fall between your restrictor and manifold or, in boosted applications, between your turbocharger/supercharger and manifold. Common solutions include actuation by throttle cable or by electronic throttle body (ETC or drive-by-wire).

Throttle form factors

now that I think about this, I think the rabbit hole details for throttle like cabling and non-butterfly throttles should get a separate page - will do later if y'all dont (-simon)

Cabling

If using a cable actuated throttle, the choice and routing of cable are important considerations. A push-pull cable has negligible stretch/flex over time and will give the greatest consistency [citation needed for strecth comparison].

Other popular choices are shifting and brake cables used on bicycles. [structure of bike brake cable v shifter cable]. A brake cable will always have some stretch, and a thicker gage will stretch less.

Cable fittings are either swage or swageless. Swage fittings are permanently attached by crimping (swaging). Swawgeless fittings can be attached to the cable in a number of ways including set screws or collets. [citation for fittings] Swageless fittings allow for a degree of adjustment as the cable stretches.

[insert image of swageless v swage fittings]

Dry lube like graphite or molybdenum disulfide are the best go to for high quality cable sheathing. However, if the cable is in a wet/humid environment or the sheathing is old or slightly damaged, a liberal dose of a high quality oil such as motor oil is desirable[ciitation needed]. Non-synthetic oils like mineral oil can degrade the cable housing [citation needed]. WD-40 may also degrade the housing and will dissolve the lubricant applied to the cable by the manufacturer [citation needed].

Further reading here: <a href="https://www.sheldonbrown.com/cables.html">https://www.sheldonbrown.com/cables.html</a>

add routing info also

ETC

Main page: Electronic Throttle Control

overview and driving rationale how it fits into system not specific design info

Intake tuning

(I dont know where this should go: The intake manifold typically runs from the plenum to the cylinder heads / air intake ports on the engine. It's design can be adjusted to increase performance using the tuning methods below. The manifold also contains ports for the fuel injectors. (i think this is a great place for it, maybe a section about intake structure above this to clear up all the terminology? -simon)

Maybe make an intake system terminology section? I agree though, probably better to have more than less information

Tuning takes two forms for the intake manifold: the first is in modifying the length of the manifold (ram tuning) and the second is in modifying the shape of the manifold (including Helmholtz resonators).

Ram tuning

The basic principle behind ram tuning is that a cylinder intakes air at a particular frequency, i.e. a cylinder only takes in air for a quarter of a four stroke cycle, meaning that there is a stop-starting of the flow of air into the cylinder. This occurs at a frequency dependent on the rpm of the engine, hence ram tuning is done to optimize performance at a selected rpm. The way in which it is implemented is to modify the length of the manifold such that the pressure wave formed on each cycle travels along the manifold and is reflected back, arriving just as the cylinder completes the cycle and takes in its next lot of air. This means that the pressure at the inlet will be higher whenever the engine needs air, giving better volumetric efficiency for the engine.The parameters to adjust regarding ram tuning is the diameter and length of your intake runner, in port injection applications, this is also known as the injector body.

In more complex ram tuning applications, actuated baffles can be created to vary engine torque curve. This is done on many production cars to allow different behavior at low and high RPM.

Trade-offs

Pros

• Relatively simple system
• Allows for movement of your torque curve
  

Cons

• Simulations are often inaccurate and may require on vehicle testing to confirm optimal performance
• Can only tune to one optimal frequency, unless baffles are integrated

Helmholtz resonators

Helmholtz resonators work by having a thin neck followed by an open cavity attached to the engine's intake. Their design result in low pressure at the neck, sucking in more air, and resulting in higher pressure air in the cavity, which can then feed the engine. Both ram tuning and Helmholtz resonators are simple methods to increase engine efficiency. Helmholtz resonators are most effective in single cylinder systems, as the flow through the intake can be dominated by pulsed flow characteristics at high rpms [citation definitely needed]

Plenum

• why we have plunem
• sizing considerations
• shape/ form factor?
  • conical spline
  • top/center feed
  • side feed
  • <a href="http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.582.6654&rep=rep1&type=pdf">http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.582.6654&rep=rep1&type=pdf</a> source for intake shape
  • dual plenum
  • variable volume

Restrictor power limit derivation

The competition requires all air entering the engine to first pass through a 25mm diameter hole. This restrictor places a theoretical upper limit on the power that can be generated by a naturally aspirated engine. The upper limit is derived using the general equation for ideal compressible gas flow:

A	Area
R	Gas Constant
$T_{t}$	Total Temperature
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \gamma}	Specific Heat Ratio
M	Mach number
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle P_t}	Total Pressure

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \dot{m} = \frac{A*p_t}{\sqrt{T_t}}*\sqrt{\frac{\gamma}{R}}*M*(1+\frac{\gamma-1}{2}*M^2)^{-\frac{\gamma+1}{2(\gamma-1)}}}
when M becomes 1, the flow is considered choked. The equation becomes:
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \dot{m} = \frac{A*p_t}{\sqrt{T_t}}\sqrt{\frac{\gamma}{R}}(1+\frac{\gamma-1}{2})^{-\frac{\gamma+1}{2(\gamma-1)}}}
With some basic assumed values at sea level, the maximum mass air flow through the restrictor can be found:

A	3.14 e-4	m^2
R	0.286	kJ/kg-K
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle T_t}	300	K
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \gamma}	1.4
M	1
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle P_t}	101.325	kPa

[citation needed for above values?]

Plugging these into the equation above yields a steady state mass flow rate of 0.074 kg air per second
If we assume an AFR of 13.1 (typical lambda for high torque for NA engines[citation needed]), and a Q_LHV of 46 MJ/kg [citation needed], the mass air flow yields a power limit of 265.5 kW or 356 hp total energy output. If the thermal efficiency of the engine is assumed to be a nominal 33%, the maximum available mechanical power is 88.5 kW or 118 horsepower with 100% volumetric efficiency.
This limit can be exceeded by increasing the upstream pressure to greater than 1 atmosphere. This pressure increase is called forced induction.

Forced induction

Forced induction is done by utilizing a compressor to increase the pressure seen in your manifold/plenum, leading to increased engine power and efficiency. This is accomplished by the higher manifold pressures being able to force more air into the cylinder/s on each intake stroke. The increased air in the cylinder means you can burn more fuel and maintain the same air-fuel-ratio. A denser charge will also combust faster, yielding greater energy utilization and efficiency. Common methods of implementing forced induction is by turbocharging, supercharging, or procharging. Within FSAE, a fair number of teams run forced induction, but the majority remain naturally aspirated. [citation?, not sure how to cite that I saw like 5/100 at competition in Michigan and Lincoln, maybe the competition handbooks?|| i can go through my FSAE MI 2018 handbook this weekend, but its only 120 teams, out of the hundreds in the world, maybe a FB and reddit poll?]

Turbocharging

Theory

Turbo system diagram

A turbocharger works by compressing intake air by harvesting thermal energy, traditionally discarded, from the exhaust. The general flow of air through a turbocharged system can be seen to the right. Theoretically, the higher plenum pressure you can run and not produce knock, the more power you can extract from your engine package. The liability to knock is based upon many factors, including but not limited to, fuel choice, fuel injection location, and compression ratio.

Cooling charge air

The charge air cooler, also known as an intercooler, is designed to lower your charge air temperature. The intake air temperature increases due to compression, according to the equation. Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle (P_2/P_1)=(T_2/T_1)^{\gamma/(\gamma-1)}} , where gamma is 1.4 for air. This equation must be used with absolute pressure and temperature.Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle P_2/P_1} is also known as pressure ratio. For example, a pressure ratio of two (1 atm to 2 atm) will lead to a 20% increase in intake air temperature. This means for an inlet temperature of 20C, your plenum temperature will be approximately 85C. If you run low boost, intercooler may be able to be avoided. Alternatively, injecting E85 upstream of the runner to cool the air via the evaporation may be feasible. This is only done due to the high latent heat of evaporation and low evaporation temperature for E85. This method is beneficial as it provides cooling and well mixed air fuel mixture, howeverrequires an extremely solid tune otherwise your plenum is liable to turn into shrapnel.

Blow off valve

The purpose of a blow off valve (BOV) is to control your plenum/manifold pressure and prevent excess boost. This works in conjunction with a wastegate to manage plenum pressure to your desired pressure.

Supercharging/Procharging

ETS pls

Drum Chargers

p sure no one has done it in fsae, but they're out there and meme-worthy enough for a paragraph