The Diesel engine internal mixture formation makes use of a specific amount of fuel, which is injected towards the end of the compression either indirectly into the side combustion chamber or directly into a dent in the piston crown, thereby initiating the combustion. The mixture formation of the Diesel engine takes place always in the combustion chamber, the petrol engine features both internal and external mixture formation.
The diesel engine holds for every operating status at least 30 to 40% more air than needed for the combustion. Because the air is highly condensed, it is injected with very high pressures (for some systems more than 2000 bar). Due to the ever harsher exhaust gas regulations mechanical-hydraulic systems for the regulation of the fuel injection timing and injection amount were substituted by electronic systems. An engine driven pump still generates the high injection pressures. In principle, the diesel engine internal mixture formation and the petrol engine internal mixture formation are not that different. The main difference is that the petrol engine still makes use of an ignition system. Thus, the direct petrol injection can also occur at the beginning of the compression stroke or during the induction stroke. In addition, there are the substantially lower injection pressures, featuring roughly 100 bar.