Petrol and Diesel engines, what's the difference?

16th Nov 11 13:35<< Go back to news

Petrol and Diesel engines, what

In the 1970’s diesels were advertised as an alternative to petrol engines, however the early engines were loud and created a lot of pollution but over the past 30-40 years there has  been vast improvements in both performance and cleanliness of the diesel engine. The direct injection devices are now controlled by advanced on-board computers who monitor fuel combustion increasing the efficiency and reduction the emissions of the engine. Refined diesel fuel engines such as ultra sulfur diesel (ULSD) will lower the amount of harmful emissions and upgrading of the engines to a cleaner fuel is becoming a simpler process. Fuel efficiency is not the only improvements to be made to diesel engines other technologies such as CRT particulate filters and catalytic converters burn soot and reduce particle matter, carbon monoxide and hydrocarbons which are harmful to both humans and the environment.


One of the main differences between petrol and diesel engines is the fuel injection process; most cars use either port injection, which inject fuel just before the intake stroke (outside the cylinder) or a carburetor, which mixes air and fuel before the air hits the cylinder.  Diesel engines use direct fuel injection meaning that the diesel fuel is directly injected into the cylinder, however if all the fuel is loaded into the cylinder during an intake stroke and then compressed, the compressed fuel/air mixture limits the ratio of the engine. If it compresses the air too much, the fuel/air mixture spontaneously ignites and causes knocking, which can damage the engine.


The injector on a diesel engine is not the most complex component and can vary greatly as it has been the subject of a lot of experimentation in development; this means that engines can vary greatly depending on the make and model; in one engine there could several sites where the injector could be located, all of which can be completely different to that of another engine that has the output specifications. An injector has to be able to withstand the temperature and pressure inside the cylinder whilst delivering a fine mist of fuel.


Getting the fuel mist circulated evenly within the cylinder is also an issue so diesels have been fitted with special induction valves, pre-combustion chambers or other devices, all with the aim of swirling the fuel/air mixture around the combustion chamber to improve ignition and the combustion process within the engine itself.


If this has ignited your interest then see our range of Bosch and Delphi diesel courses, course are between 1-3 days and cost between £150- £450 (not including BCS discount).

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