Advanced combustion for low emissions and high efficiency Part 2: Impact of fuel properties on HCCI combustion
A broad range of diesel, kerosene, and gasoline-like fuels has been tested in a single-cylinder diesel engine optimized for advanced combustion performance.These fuels were selected in order to better understand the effects of ignition quality, volatility, and molecular composition on engine-out emissions, performance,and noise levels. Low-level biofuel blends, both biodiesel and ethanol, were included in the fuel set in order to test for short-term advantages or disadvantages.
The diesel engine optimized in Part 1 of this study included practical and cumulative engine hardware enhancements that are likely to be used to meet Euro 6 emissionslimits and beyond, in part by operating under conditions of Homogeneous Charge Compression Ignition, at least over some portions of the speed and load map.
The centre of combustion was matched for each fuel by adjusting the fuel injection timing. This simulates the performance of a future advanced engine operating with closed loop combustion control using an in-cylinder pressure sensor. The warmed up engine could be run successfully on a wide range of diesel, kerosene, andgasoline-like fuels, including part-load and full-load operation, with diesel-like efficiency.
NOx emissions at or below Euro 6 emissions limits were achieved without the use of a NOx after treatment system. PM emissions were also low but a diesel particulate filter would be needed to reach Euro 6 limits and below. HC and CO emissions increased but were within the range that could be treated with a diesel oxidation catalyst.
Fuel properties had a substantial effect on PM emissions, consistent with the wide range of fuels investigated. In general, PM emissions decreased with increasing ignition delay, higher volatility, and lower aromatics levels of the fuel but the relative effects varied depending upon the engine operating conditions.
This study has investigated engine performance and emissions for a warmed-upsingle-cylinder bench engine only. Additional work would be needed to investigate engine performance under transient and cold start conditions.