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Diesel Engine 2

Injection methodType of vehicle
Common RailAlmost all passenger cars
Few trucks
Pump injector
Almost excl. trucks

For operating a diesel engine it is not strictly necessary to have an electric system (except for the starter)). Only diesel engines for passenger cars and vans are in need of a pre- and even more importantly an afterglow system. All diesel engines (2007) feature either a Common rail system or a pump injector respective pump-pipe- injector system.

Colder exhaust gas, worse heating

The average working pressure (average over all 4 strokes) may surpass 10 bars for modern diesel engines because of the high compression and the high combustion end pressure. Because the diesel engine compresses higher, it releases during the power stroke more space for the exhaust gases. Therefore, the exhaust gas temperatures as compared to the petrol engine are lower for the diesel engines, reaching 500°C - 600°C. Due to its efficiency it also delivers less heat to the cooling system.

Noisy cold starting takes more time to reach operating temperature

When the engine is cold, ignition delay takes place, meaning the time span between injection and the actual combustion of the fuel (normally 1 ms) increases. The fuel burns down abruptly at the end of this time span. This causes an increased noise level, also with modern engines. Therefore, and in order to improve the exhaust gas quality modern glow systems still continue their operation for some time after the cold start.

Idle speed- and maximum speed always controlled

The diesel engine requires a preset idle running speed and especially a preset maximum speed, having a minimum excess of air of 40 % also with high speed, in contrast to the petrol engine. Both pictures on top identify typical details of modern diesel engines. The piston originates from a charged truck diesel engine. It is recognizable by the gap in the front below for the oil hose nozzle. The second picture on top displays the cylinder head of a three-cylinder passenger car diesel engine. Extraordinary is that it features double overhead camshafts with four valves and centrally arranged common rail injectors.

Always excess air, Lambda 4 and higher

The smallest passenger car diesel engines can manage a thermal efficiency of approx. 44%. Large, slow-running ship diesels are even better. They manage a specific consumption of 160 - 170 g/kWh and are even more economic because they may also burn thicker fuels (heavy oil) outside the harbor. 08/08