Transient Control of HCCI Through Combined Intake and Exhaust Valve Actuation

This doctoral thesis is about controlling the combustion timing of the combustion concept Homogeneous Charge Compression Ignition, HCCI, by means of variable valve timings. The HCCI research usually is regarded to have started in Japan during the later part of the 1970´s. The world of HCCI has since grown and HCCI is of today researched worldwide. Of particular interest from a Swedish point of view is that Lund Institute of Technology has emerged as one of the world leading HCCI laboratories. The idea with HCCI is to combine the Otto and Diesel engine. As in an Otto engine the charge is premixed but as in a Diesel engine the operation is unthrottled and the compression heat causes the ignition. The combustion that follows the ignition takes place homogeneously and overall lean. The result is ultra low NOx and particulate emissions combined with high total efficiency. A difficulty with the HCCI-concept is that it only works in a narrow area and that there is no direct way to control the Start Of Combustion, SOC. Out of this follows that timing/phasing of the combustion is one of the main difficulties with HCCI combustion concepts. This is particularly emphasized during transient operation and calls for feedback control of the combustion timing. This work investigates one method, the variable valve timing, to achieve feedback control of the combustion phasing. From the work it can be concluded that the variable valve timing can control the combustion phasing during engine transients. In order to improve the performance a non-linear compensation from ignition delay to valve timings has been suggested, incorporated in a control structure and tested in engine test. The engine test has been performed in a single cylinder engine based on a Scania truck engine. The speed range from 500 to 1750 rpm and the load range 1.26 and 10.5 bar of netIMEP has been covered with fair transient performance.