Fuel

Internal combustion engines can use a variety of fuels, the fuels available at US competitions are gasoline of octane ratings 93 and 100, and E85. Fuels available in FS competitions are 98RON gasoline and E85 . Fuels and the fuel system are covered in IC.5 of the FSAE Rules, and CV 2 in the FS rules. No fuel additives can be used

Chemistry

Gasoline

Although the gasoline supplied at the pump, and in US competition is 5-10% ethanol (check about in other countries), gasoline is typically approached chemically as pure octane.
$2{\text{C}}_{8}{\text{H}}_{18}(l)+25{\text{O}}_{2}(g)\rightarrow 16{\text{CO}}_{2}(g)+18{\text{H}}_{2}{\text{O}}(g)$

if we use atomic weights for carbon, hydrogen, and oxygen, we find that 2 mol of octane is 224 grams, 25 mol of oxygen is 800 grams which comes from 3809 grams of 21 percent air. This yields an air fuel ratio of 17.

Since gasoline is not pure octane and air is not exactly 21% oxygen. Experimentation yields the stoichiometric ratio of 14.7 grams of air per gram of fuel.

Ethanol

The ethanol used in competition is E85, nominally 85% ethanol and 15% gasoline,.

System Design

Fuel Storage

I.C.1.2 Packaging Restrictions

The fuel tank design rules can be found in IC.5.2 for FSAE and CV 2.3 for FS.

There are two main compromises that the fuel storage system must navigate. The first is Quantity of Fuel. A car will always be faster with less weight, but cutting too close to the minimum fuel level for your car can lead to disastrous consequences such as running out of fuel or temporary fuel starvation, as well as minor inconveniences such as cg changing with fuel level. The second compromise is Fuel Sloshing. As the car accelerates, the fuel itself can move about in the tank, possibly uncovering the fuel pickup and making the car more difficult to drive. Combatting this usually involves a system of internal baffles as well as tank geometry, but the cost is weight, CG height, and the possibility that you design a tank that prevents the fuel from making it back to the pickup fast enough to supply the engine when needed.

(probably more compromises that im leaving out)

Volume Determination

The minimum quantity of fuel should be enough to barely finish the endurance race at competition. However, this limits the functionality of the car by limiting run time, and increases the likelihood that you will run out of fuel early. The quantity of fuel used in an endurance competition should be determined by experimental data, but can be estimated based on past usage, or usage of similar teams, or if masochistic, be predicted based on average speed of the vehicle, the track length, and the consumption of your engine.

For the FSAE Michigan competition, out of the 25 teams that finished endurance, the average fuel consumption is as follows:

Average 2021 FSAE Michigan Fuel Use and Efficiency Score by Type

	93 Octane	100 Octane	E85
Fuel Used	3.98 L	4.3 L	5.6 L
Efficiency Score	76.4	66.8	77.3

• ways to pick factor of safety - should be on own page for FoS Choice, the strategy is relevant to everything in life
• Fuel Competition Strategy -Emily wants own page for comp strat

Since FSAE and FS considers how much fuel is used as well as how fast each car goes, the cost of fuel in terms of competition score must be considered. There are many ways to analyze the impact of the fuel usage on the competition score. A simplistic, black box analysis is shown below using the 2021 Michigan Efficiency Event scores. With the cost of fuel in hand, one can weigh the pros and cons of burning more fuel to go faster or even the advantages of each fuel type.

Points per L Fuel used in 2021 Michigan Competition

fixed volume only

Fuel Sloshing

• kinda meme-y
• very team dependent, need to get ur own data, kiddo

Rigid Container

mounting

• cannot be stressed or loaded in any way by frame - no 3 hard points for mounting

material
form factor (exterior and interior)

Bladder

just pour the gas in a kroger bag and let it flop in the wind /s

must be enclosed by a non-flexible container that is rigidly connected to the chassis and may be load bearing

Fuel Lines

Material	Internal Diameter [in]	Pressure [psi]	Cost [$ per foot]	Weight [lb/ft]	Minimum Bend Radius [in]	Supplier	Notes
Hard Lines
Aluminum	3/8-1/2 (OD)	250*	2+			Russell	link *pressure rating is wall thickness dependent
Aluminum (0.035 wall thickness)	1/4-5/8 (OD)	200*	0.68	for 3/8": 0.043 (.651g/cm)		Summit	link *pressure rating not specified formally, only mentioned in Q&A with conflicting answers, trust with caution
Nickel/Copper Alloy (0.028 wall thickness)	.132-0.319 (__ -3/8 OD)	unspecified	1.28	for 3/8": 0.012 (.175g/cm)		Summit	link sold as pressure rated comparable to mild steel brake line
304 Steel (0.028 wall thickness)	.257-.319 (5/16-3/8 OD)	3500	2	for 3/8": 0.010 (.156g/cm)		JEGS	link
Soft Lines
Nitrile Rubber*	3/8	50	0.88			JEGS	link
Nitrile* (Neoprene* cover)	1/8	50	0.8			Dayco	product details cannot buy direct
Buna-N*	3/16+	50	1.1		1.25	McMaster	link yarn reinforced
Buna-N*	3/4+	150	7		3	McMaster	link steel wire reinforced
Braided Lines
Nitrile Rubber* and Steel	1/4+	50	3.50+			Spectre	link
Nitrile Rubber* and Stainless Steel	0.22+ (4AN+)	1000	6+		2	Pegasus	link
PTFE and Stainless Steel	0.27+ (4AN+)	1320	11.3+		0.75	Pegasus	link
PTFE and Aramid	0.27+ (4AN+)	1320	21.3+		0.92	Pegasus	link
PTFE and Polyester	0.38+	305+	15.8+		2	Pegasus	link

* not compatible with e85

Comparison of Line Types

Quality	Hard Lines	Braided Lines	Soft Lines
Weight			-
Cost		-	+
Cost Tables (FSAE)		-	+
Manufacturability	-		+
Pressure Capacity	+*		-
Reusability**	-		+
e85 Compatibility	+		-
\*Depends on wall thickness, see table above \**New design or small adjustments that need to be made

Pump and Pressures

Low Pressure

under 10 bar
depends on injectors, we ran 3 bar, not sure what other people did
low pressure if for tbi and pi

Fuel Rail

critical fasteners

High Pressure

systems running at or above 10 bar high pressure is for di
FSAE - Fuel lines must be stainless steel hard-line or "Aeroquip FC807 smooth bore PTFE hose with stainless steel reinforcement and visible Nomex tracer yarn" (although you can run something similar if you get approval before comp)
supply before boost pump is considered low pressure

Fuel Rail

must be able to withstand max force not including cyl pressure
critical fasteners

---

talk about filters here? contribute to pressure loss...

Injectors

Placement

Throttle Body Injection

basically electornic carb

Port Fuel Injection

Fuel Injected into the ports just before entering the combustion chamber. Usually leads to well mixed charge [citation needed]

Direct Fuel Injection=

big boys do this [citation needed]

Classification by Resistance

Low Resistance

Usually 0.5 - 5 Ohm. Also called "peak-and-hold-injectors". From this name you can directly infer the mode of operation. In the beginning the ECU has to give a high current to the valve to open it quickly. This is the peak. Then a lower current is sufficient to keep the valve open. A common ratio of the currents is 4:1.

However, for this the ECU must also have a controller that can supply the different currents. The advantage of this system is that due to the high current at the beginning the valve can be opened very quickly. However, this is no longer necessary nowadays, because even valves with high resistance can provide the necessary flow.

High Resistance

Ususally 8 - 15 Ohm. Also known as a "saturated drive injector". These are much easier to control, as only the circuit has to be closed and the resistance of the valve controls the current.

Firewall

Main page: Firewall

Fuel Strategy

Efficiency

BSFC

link for calc citations
copying from old school notes so i'll have to add context later -simon

this is for finding fuel consumption (mpg or equivalent) w bsfc chart

P_me (mean effective pressure)

n_mot (motor speed)

i_G (gear ratio for selected gear)

i_sec (FDR)

r_dyn (dynamic radius of tire)

V_d (displacement volume of engine)

i (constant for 4 stroke)

F_req (tractive force required)

$p_{me}={\frac {(2\pi *T_{motor,required})}{(V_{d}*i)}}={\frac {(2\pi )}{(V_{d}*i)}}*{\frac {(F_{req}*r_{dyn})}{(i_{G}*i_{sec})}}$

$n_{motor}={\frac {Velocity*i_{G}*i_{sec}}{2\pi *r_{dyn}}}$

be (fuel consumption) usually experimentally determined

$B_{time}={\frac {b_{e}*p_{me}}{\rho _{fuel}}}={\frac {b_{e}*p_{me}*V_{d}*n_{motor}*i}{\rho _{fuel}}}$

$B_{distance}={\frac {B_{time}}{V}}$

i = 0.5 for 4-stroke engine