Multivariable air path and fuel path control for a Diesel engine with homogeneous combustion

Abstract

The development of the upcoming automotive diesel engine generation is predominated by the difficult challenge of reducing emissions while simultaneously improving efficiency. Near the use of alternative bio-fuels, low-temperature premixed combustion processes have been demonstrated to be a feasible solution for this problem. Increasing the mixture homogenization and reducing the combustion temperatures provide decreasing NOx and smoke emissions. However, the large attentions that have been given to this combustion process during the end of the last century have been lowered by drawbacks such as high combustion instability and poor fuel conversion of HCCI combustion (Homogeneous Charge Compression Ignition). Large difficulties have been also encountered in the application of these processes for commercial engine applications. A compromise has been found by providing only a partial homogenization of the fuel mixture by timing the injecting event towards the end of the compression stroke. This solution has shown greater potential for series engine applications, but problems related to the control of the combustion process still remain the major drawback of this technology. This is mainly due to the high system sensitivity to small changes in the charge composition. Moreover the use of this combustion process is limited at low to middle load ranges and a solution for switching to conventional combustion mode must be found. Particularly during transient engine operation, the realization of a torque-neutral switching procedure is a particular difficult task.