Experimental Investigation of a Control Strategy Based on Combustion Stability and Combustion Phasing for a Multi-Cylinder Engine with Fueled Pre-Chambers and Cylinder Pressure Transducers

One way of increasing the efficiency of a gasoline engine is to operate it in lean-burn mode. However, a lean mixture in the combustion chamber reduces its ignitability, which leads to poor combustion stability and even misfires. This investigation presents a solution to this problem using an active pre-chamber for each cylinder, into which fuel can be injected separately and in which ignition takes place. This increases the ignition energy in the main combustion chamber, thus enabling stable combustion. Cylinder-specific feedback control of the fuel quantity injected into the pre-chambers was implemented on the basis of measured cylinder pressures so as to compensate for injector component deviations, achieve maximum efficiency, and prevent increased emissions. Since combustion delay and burn duration are dependent on the fuel mass injected into the pre-chamber, an additional feedback control for the center of combustion (MFB50) was integrated along with the fuel quantity controller. Combustion stability and MFB50 were determined from cylinder pressure sensors. Correct functionality of the two controllers was demonstrated exemplarily at a stationary operating point at 2000 rpm, with an indicated mean effective pressure of 8 bar and an air-fuel equivalence ratio λ = 2. Use of the controllers was shown to improve the combustion stability of all cylinders and to equalize the MFB50. With both controllers activated, the brake thermal efficiency (BTE) was improved by one percentage point, which corresponds to a relative improvement of 2.3%.