The BPI Flame Jet Concept to Improve the Inflammation of Lean Burn Mixtures in Spark Ignited Engines

Spark ignited engines with direct injection (DISI) in fuel stratified mode promise an increase in efficiency mainly due to reduced pumping losses at part load. However, the need for expensive lean NO_x catalysts may reduce this advantage. Therefore, a Bowl-Prechamber-Ignition (BPI) concept with flame jet ignition was developed to ignite premixed lean mixtures in DISI engines. It is characterised by a combination of a prechamber spark plug and a piston bowl. An important feature of the concept is its dual injection strategy. A pre injection in the inlet stroke produces a homogeneous lean mixture with an air fuel ratio of λ = 1.5 to λ = 1.7. A second injection with a small quantity of fuel is directed towards the piston bowl during the compression stroke. The enriched air fuel mixture of the piston bowl is transported by the pressure difference between main combustion chamber and prechamber into the prechamber. After the ignition of the mixture strong flame jets penetrate the main combustion chamber and initiate the main combustion process.

Numerical and experimental investigations were carried out in a modified 3-valve single cylinder engine. The in-cylinder gas flow including the mixture process in the main combustion chamber and in the prechamber was investigated by CFD simulation so that the local mixture composition could be predicted. With extended test runs and measurements the functionality of the BPI concept has been proved. The BPI flame jet concept operates in all areas of the engine map and even with all kind of DISI processes.