Supercharging HCCI to Extend the Operating Range in a Multi-Cylinder VCR-HCCI Engine

The operating range in terms of speed and load for a natural aspirated Homogenous Charge Compression Ignition (HCCI) engine is restricted by a lack of dilution at high load and a poor combustion at low load. Today HCCI is seen as a part load concept, but the operating range for vehicle applications should at least cover contemporary driving cycles, without switching to a conventional Spark Ignited (SI) combustion mode. Dilution with air at high load can be increased by supercharging, but with the drawback of parasitic losses or pumping losses decreasing the brake efficiency and by that one of the benefits of HCCI.

The effect of advancing the combustion phasing and throttling the inlet air on the combustion efficiency at zero loads is investigated. The combustion efficiency increases drastically in both cases. The increase in the combustion efficiency overcomes the drawbacks of the early combustion phasing in the first case and the pumping losses in the second case.

The HCCI operation range with both mechanical supercharging and simulated turbocharging is investigated and compared with a natural aspirated SI with gasoline as fuel. The operating range can be more than doubled with supercharging and higher brake efficiency than with a natural aspirated SI is achieved at the same loads. Mechanical supercharging is however not an option with HCCI combustion, due to the high parasitic losses.

The test engine is a 5 cylinder in-line engine with Variable Compression Ratio (VCR) and displacement of 1.6L.