Transient Control of HCCI Through Combined Intake and Exhaust Valve Actuation 2003-01-3172
Homogeneous Charge Compression Ignition, HCCI, has the attractive feature of low particulate emission and low Nitrogen Oxides, NOx, emission combined with high efficiency. The principle is a combination of an Otto and a Diesel engine in that a premixed charge is ignited by the compression heat.
One of the main challenges with the HCCI combustion system is to control the Start Of Combustion, SOC, for varying load and external conditions. A method to achieve this on a cycle-by-cycle basis is to vary the valve timing based on a feedback signal from the SOC of previous cycles. The control can be achieved with two basic valve-timing strategies, named the Overlap- and the IVC-method. The Overlap-method works by trapping of residuals while the IVC-method affects the effective compression ratio. These methods have in an earlier paper been verified to work one at a time to control SOC during engine transients . In this work the two strategies are incorporated into one controller, thereby allowing the operational window to be widened.
Engine tests are conducted on a single cylinder engine equipped with a hydraulic valve system. Results shows that SOC successfully can be controlled and that the operational window is widened by aid of the combined controller. Net Indicated Mean Effective Pressure, net IMEP, between 1.26 bar and 10.5 bar has been tested in the 500 rpm to 1750 rpm speed range. The principles behind the combined controller are discussed from an engine perspective. The control performance is reported and the area of operation for the two strategies is evaluated.
The work described forms the basis for further studies of HCCI control. The long-term goal of the research is to develop model based control strategies for HCCI engines using variable valve timing to achieve transient control on a cycle-by-cycle basis.