When is fuel typically injected into the cylinder of an engine?

Fuel is typically injected into the cylinder of an engine just before top dead center (TDC) to ensure optimal combustion. This timing is crucial because it allows the fuel to mix with air effectively and be ignited at the right moment. Injecting fuel just before TDC maximizes the pressure and temperature in the combustion chamber, resulting in a more efficient and powerful combustion process.

In a four-stroke engine cycle, the combustion process requires precise timing to ensure that the air-fuel mixture ignites just as the piston reaches its highest point. This ignition timing leads to a rapid increase in pressure, which forces the piston down during the power stroke.

The other choices represent points in the engine cycle where fuel injection is either inefficient or ineffective. For example, injecting fuel after TDC or at bottom dead center (BDC) would lead to a delay in ignition, resulting in incomplete combustion and reduced engine performance. Fuel injection during the crankshaft rotational cycle without the timing relation to TDC can also lead to suboptimal combustion, making precise timing essential for engine efficiency.