Abstract
Keywords - Controlled Auto Ignition, Electromechanical Valve Train, Variable Valve
Train, Load Exchange Control, Combustion Process Development
Abstract - Controlled Auto Ignition (CAI) as a promising future combustion process is a concept to strongly reduce fuel consumption as well as NOX emissions. Depending on the variability of the valve train and additional technologies like direct injection or supercharging the limited engine map area for this technology can be strongly influenced. In combination with a supercharging system tuned for enhanced lean burn capability a significant increase of compression ratio can be realized along with significant reduction of fuel consumption.
The investigations presented in this paper were done on an engine equipped with electro-mechanical valve train (EMVT), featuring port fuel injection and gasoline direct injection.
They show that the electromechanical valve train is an excellent platform for developing the
CAI process. Controlled Auto Ignition has been realized with port fuel injection in a speed range between 1000 and 4500 rpm and in a load range between approximately 1 and 6 bar
BMEP (about 5 bar BMEP for pressure gradients lower than 3 bar/°CA) depending on engine speed. In a wide range of the engine map NOx emission reduction of 9099 % was realized, fuel consumption in the New European Driving Cycle (hot test) can be reduced by approximately 15 % (w/o cylinder deactivation) compared to a standard production engine.
Tests performed with gasoline direct injection have shown a significant increase of maximum possible load for CAI. Additionally fuel consumption can be further reduced during CAI operation with direct injection. Further potentials can be seen using split injection and multi stroke operation. Especially 2-stroke and 6/8-stroke operation with dual combustion show high potential for fuel efficiency and an extension of the Controlled Auto Ignition map area.
In the 6/8-stroke with dual combustion mode a combination of stratified combustion process and homogenous combustion process with Controlled Auto Ignition is realized.
Due to cycle synchronous control of valve timings, injection and ignition offered by the
EMVT changes between the operation modes CAI and SI as well as between different CAI operation modes can be realized without misfire and negative torque response.
Based on investigations with the EMVT engine the necessary variability of a mechanical valve train as well as the requirements for transient behavior can be identified, giving distinct targets for a mechanical variable valve train enabling CAI. Possible mechanical valve train concepts to realize the Controlled Auto Ignition Combustion Process are presented.