A higher cetane number means a shorter ignition delay and a smaller amount of fuel in the combustion chamber when the fuel ignites. This pattern was developed as a general representation of transit vehicle operation in a downtown business district and consists of 14 identical segments. Each segment includes 10 seconds of acceleration, 18.5 seconds of cruising at 20 mph, 4.5 seconds of deceleration, and 7 seconds of idling. Total driving distance is two miles. The engine's electronic timing regulates fuel-injection timing and quantity according to data from sensors on the camshafts and crankshafts, so that compression and injection occur independently.
Fuel is injected only as needed, which reduces fuel consumption and emissions.
Rapidly compressing the air within the cylinders generates enough heat to ignite the fuel as it is injected. This is why diesel engines do not need spark plugs for ignition. A standardized single-cylinder, overhead valve, variable compression ratio engine used throughout the world for basic research into exhaust emissions and the suitability of alternate fuels. A diesel engine differs from other internal-combustion engines, such as gasoline engines, in that it employs no ignition devices, such as an electric spark. For this reason, it is often called a compression-ignition engine.