Question

2. (10 pts) Power and torque curves are given for two V8-3.6L engines, one of which is running on gasoline, and the other one is running on diesel. From the power-torque curves, please determine which one of the following engines is diesel. Please give three reasons for your selection Engine A Engine B Power Torque INml Power Torque [Nm] 5 3 Power Torque Power Torque 4000 Engine speed Crp SO Engine speed Erpm]

Answer 1

Engine B is diesel engine because of the following reasons:

1.The most obvious difference is maximum torque. The diesel engine produces maximum torque at around 2000rpm, whereas the petrol engine does this at over 4000rpm. The initial surge in a diesel is followed by a sharp reduction in engine torque, which encourages the driver into a gear change. The petrol engine, by contrast, produces a relatively flat torque curve, which gives a continuous long pull feel to its acceleration.

2.The diesel engine has higher peak and average combustion pressures and this means that the piston/crank assembly has to be more substantial and therefore heavier, which limits the maximum speed of the engine. Speed is also limited by a slower combustion process. whereas Petrol engines are lighter and with lower cylinder pressures. They produce less torque but gain their superior power by producing it faster.

3.As a consequence of a higher compression ratio (longer stroke), diesel engines produce more torque which means you get more acceleration off the line. This is also the main reason for diesel cars having a much smaller power band, so you generally get more torque but spread over a smaller area.