Homogenous charge compression ignition (HCCI) engines offer a great potential in achieving high thermal efficiency and extremely low NOx at the same time. However, control of combustion phasing over a wide speed and load range has been a challenge, especially during transient operations.
This paper describes work conducted at the National Vehicle and Fuel Emissions Laboratory, which explores the potential use of an HCCI engine as a power plant for a hybrid vehicle. A four-cylinder, 1.9 L commercial diesel engine was modified to operate with port-injected regular grade gasoline in HCCI mode. The combustion phasing is controlled by a combination of boost, EGR and thermal management as a function of engine speed and load.
As a stand-alone unit, the engine has demonstrated a wide operation range with efficiency like that of a diesel engine and NOx below 0.2 g/kWh. At room temperature, the engine starts in SI mode and then transitions to HCCI in about 25 seconds. If the engine is warm (oil temperature is above 50°C), it starts directly in HCCI mode. The engine can also operate and make transitions smoothly along a 3.5 to 40 kW power curve when the engine is warm. Work to expand the power range and reduce the transient time is underway. However, the capability of the engine as demonstrated would allow it to be utilized as a power plant for a hydraulic hybrid motor vehicle.