Diesel Engine 2
Injection method | Type of vehicle |
Common Rail | Almost all passenger cars Few trucks |
Pump injector Pump-pipe-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
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