How would you expect the fuel consumption and performance ou

How would you expect the fuel consumption and performance (output power and efficiency) of the engine at a part throttle setting (throttle valve partially closed) to compare to the engine at a full throttle setting?

Solution

Engine at part throttle setting, the throttle valve will allow only a percentage of air to enter the intake system. Also the intake system is now at a vaccum pressure (lower than atmospheric). In this case the power and efficiency depend on fuel, holding the throttle to not open fully will let more fuel into the system. More fuel but less oxygen to burn it, hence improper combustion leading to power loss and higher emissions, efficiency reduces.

Full throttle position will allow sufficient air into the combustion chamber however, fuel reduces as pressure is atmospheric. Efficiency will be higher, power will be higher but torque will be low.

Hence lower rpm, part throttle is better. Higher rpm full throttle.