Assume that you own a Ferrari 458 Italia. This car\'s engine has a 12.5:1 compre
ID: 518395 • Letter: A
Question
Assume that you own a Ferrari 458 Italia. This car's engine has a 12.5:1 compression ratio (very high compression ratio for a gasoline engine). On your drive to campus for Thermo class, you stop at a gas station to fill up the tank. You accidentally fill your tank with 87 octane gasoline. Upon realizing your mistake, you check your owner's manual, which specifies that the fuel should have a minimum octane rating of 91. What may happen inside your engine as a result of using the lower octane fuel? Why?Explanation / Answer
If your car is designed to burn 87, it will not burn 93 correctly. Third, your gas mileage will suffer. The inability of your engine to burn the higher octane gas correctly will cause your engine to produce less power and thus will require more fuel to perform at the same level.
Low octane fuels are less stable, and are too easily ignited at conditions present inhigh compression (or high boost) engines. This can cause early or uneven ignition of the air/fuel mixture in the cylinder, causing a distinct pinging or knocking sound.A high performance car's engine is designed to run at a high compression ratio (or under boost), resulting in high pressures in the cylinders. High octane fuels are designed to operate under these conditions by not spontaneously combusting under these high pressures and temperatures. Instead, fuel is ignited and burned by the spark plug with precise timing in the four-stroke cycle, resulting in an optimal combustion front.
Low octane fuels are less stable, and are too easily ignited at conditions present in high compression (or high boost) engines. This can cause early or uneven ignition of the air/fuel mixture in the cylinder, causing a distinct pinging or knocking sound. The sound comes from the uneven combustion front.
If you put a tank of low octane fuel in your car, chances are you won't notice the difference and it won't do anything harmful. In harder driving (freeway on-ramps perhaps), you may notice a pinging sound, and your car may not be able to produce as much power. In a bad case, it may run a bit more rough.
An engine doesn't "get used to" high octane fuel, and develop a requirement for it. However, regularly running low octane fuel in an engine designed for high performance will eventually wear on the engine and degrade longevity.