Diesel Performance Tuning
How do we increase the performance of a diesel car engine?
The main difference between diesel and petrol engines is the means by which the fuel/air mixture is introduced into the cylinder and then ignited. In the petrol engine, the fuel is mixed with the incoming air before it enters the cylinder, and the mixture is then ignited at the appropriate moment by a spark plug. At all conditions except full-throttle, the throttle butterfly restricts the airflow, and cylinder filling is incomplete. In the diesel engine, air alone is drawn into the cylinder and then compressed. Because of the diesel's high compression ratio (typically 20:1), the air gets very hot when compressed - up to 750°C (1 382°F). As the piston approaches the end of the compression stroke, fuel is injected into the combustion chamber under very high pressure, in the form of a finely-atomized spray. The temperature of the air is high enough to ignite the injected diesel fuel as it mixes with the air. The mixture then burns and provides the energy which drives the piston downwards on the combustion (power) stroke.
In a petrol engine we always need to inject extra energy to start the combustion cycle which is in the form of a spark. A petrol engine is not only fuel but also air regulated to make sure that the mixture is always 1 to 1 to keep it explosive. If we didn't regulate the amount of air in a petrol engine the overflow of air related to the fuel would not allow the mixture to be explosive any more. This also explains why a diesel engine in partial engine load needs less fuel, because the compression of the engine is not influenced by a throttle body.
In a diesel engine we don't have this problem because the air temperature and pressure are always higher (compression) which allow the diesel to self-combust. With a petrol engine you decrease the end compression in part engine load caused by the throttle body and this will decrease the compression and the efficiency of the engine.
Only the amount of injected diesel will regulate the power-output of a diesel engine. When the engine runs in low engine-load there is always a remainder of air (oxygen) that is not used for the combustion. Also when the engine is running on full load there is still a big remainder of air that is not used for combustion. Depending on the engine manufacturer this remainder is anywhere from 20% up to an astonishing 50%! When we inject extra diesel under these conditions we create extra engine power almost 1 to 1 related to the extra amount of diesel we have injected. So by regulating extra diesel we regulate extra power. The engine manufacturer keeps this remainder of air to guarantee that the engine always will run within the stated emissions and fuel consumption (MPG). Also when the car is used in countries that have ambient temperatures above 40 degrees Celsius and poor fuel quality it will still maintain its emissions level. In Europe we have very good fuel quality and almost no ambient temperatures above 40 degrees Celsius. By injecting extra diesel to "tune" the car it is possible to increase power without creating a negative outcome related to emissions (smoke).