Abstract
Keywords - HCCI, Hybrid Electric Vehicle, Control
Abstract - Diesel HCCI (Homogenous Charge Compression Ignition) is a combustion technology showing great promise for the drastic reduction of oxides of nitrogen and particulate matter from diesel engines. However, it is widely recognized that medium to high loads are not currently achievable with this combustion system. To circumvent this limitation, our implementation is a mixed-mode HCCI/DI combustion, which relies on the use of an essentially unmodified common-rail CIDI engine, coupled with a highly effective atomizer for external mixture formation. With this concept, the engine can operate in HCCI mode, HCCI/DI mixed mode, or DI mode depending on the load, and with seamless, progressive mode transition. The concept has demonstrated extremely low levels of nitrogen oxides (below 3 ppm) and smoke (FSN < 0.03) and pure HCCI operation up to an IMEP of 4.7 bar. Operation at various conditions (engine speeds, loads, boost pressures, intake temperature, EGR rates from 0-60%, etc ) have shown that this technique enables HCCI operation over a wide range of engine conditions with relative insensitivity of the combustion process to operating conditions. Furthermore, the transition from HCCI to mixed HCCI/DI to DI combustion mode is seamless, significantly enabling the controllability of such a combustion system over the entire engine operating map.
In this paper, we present a supervisory control strategy for a hybrid electric vehicle which best exploits the NOx characteristics of such a mixed-combustion mode engine, while optimizing fuel economy and meeting drivers demand. This strategy is an extension of our Adaptive Equivalent Consumption Minimization Strategy (A-ECMS) control strategy, suitably modified to explicitly minimize NOx emissions. The HEV configuration, coupled to this control strategy, allows to very effectively manipulate the operating points of the engine to be primarily constrained in the HCCI regime, with very low NOx emissions. This results in dramatically reduced NOx emissions during actual driving conditions, while retaining the high fuel economy of CIDI engines and hybrids and maintaining the performance envelop of the vehicle.