City of Miami Fire Department Driver-Engineer Practice Test 2026 - Free Driver-Engineer Practice Questions and Study Guide

In a diesel engine, ignition occurs after the air has been compressed to a high temperature, and the rapid combustion of the fuel creates high-pressure, hot gases that push the piston downward, performing the power stroke. This downward push is where the engine converts the chemical energy of the fuel into mechanical energy that drives the crankshaft. The intake stroke is about drawing air in, the compression stroke is about raising the air’s pressure by pushing the piston up, and the exhaust stroke is about expelling the burnt gases as the piston moves up. The expansion of the combustion gases during ignition drives the piston down in the power stroke, making it the correct choice.