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Fundamentals of Premixed Charge Compression Ignition (PCCI) diesel engine operation

Premixed Charge Compression Ignition (PCCI) combustion was realised in a single-cylinder research engine with a port-fuel injection. Heptane was used as the test fuel as it has a similar cetane number (60) to diesel fuel and low boiling temperature. In addition, heptane can be easily injected via a standard port-fuel injector and Heptane as the surrogate fuel. Comprehensive results were obtained using n-heptane and an engine speed of 1500rpm. The effect of compression ratios and intake charge temperature on engines performance and emission was studied in detail.

In general, the PCCI combustion of heptane is limited by its low IMEP output at low load (leaner mixture) and by the knocking combustion at high load (richer mixture) for the same amount of EGR. As EGR increases, both the low and high-load limits are reduced in terms of air/fuel ratios and over a certain percentage misfire occurs.

When one increases the compression ratio from 12:1 to 18:1, the operational range of PCCI combustion increases and the misfire limit is extended to higher EGR rates. However, the maximum IMEP value that can be obtained with HCCI combustion is reduced at higher compression ratio due to the onset of knocking combustion at a leaner air/fuel ratio. As the compression ratio increases, the combustion takes place earlier and combustion duration becomes shorter - thus the HC and CO emissions are reduced slightly.

Operational range of PCCI combustion is increased at higher intake charge temperature. The increased charge temperature also leads to earlier beginning of combustion. However, the temperature effect on combustion duration is small. Similar to the compression ratio effect, the HC and NOx emissions are lower at increased charge temperature.

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School of Engineering and Design, Brunel University
Kingston Lane
UB8 3PH Uxbridge
United Kingdom
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