Integrated simulation and engine test of closed-loop HCCI control by aid of variable valve timings

摘要

Homogeneous Charge Compression Ignition, HCCI, has the attractive feature of low particulate and low NO{sub}x 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 combustion timing/phasing 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 combustion timing of previous cycles. A combined engine and control simulation is performed. The simulations are accomplished with a commercial cycle simulation code linked with a commercial control simulation code. The simulations are iteratively verified against engine test data. Engine tests are conducted on a single-cylinder engine equipped with at hydraulic valve system that allows a high degree of freedom in choosing the valve timings. A novel very fast hybrid hardware-software system to evaluate combustion timing is described and implemented on the test bed. Combustion timing estimated with this new system has been used as feedback to control the valve timings for the oncoming cycle. The results show that combustion phasing successfully can be controlled by aid of variable valve timing during varying external conditions. Engine tests describing the control performance achieved in initial experiments are reported. Net Indicated Mean Effective Pressure, net IMEP, of up to 5.6 bar has been tested. The work described forms the basis for further studies of HCCI control.