Regulations on emissions from diesel engines are becoming more stringent in all parts of the world. Hence there is a great deal of interest to develop engine combustion systems that offer the efficiency of a diesel engine, but with low smoke and NOx. One promising approach is that of Partially-Premixed Compression Ignition (PPCI) or Low Temperature Combustion (LTC) mode. Using this approach, smoke can be reduced in compression ignition engines by promoting the mixing of fuel and air prior to combustion. NOx levels can be reduced by reducing combustion temperatures by burning leaner, pre-mixed or using EGR, exhaust gas recirculation.
The influence of fuel has also proven significant, those fuels which have proven more resistant to ignition i.e. gasoline rather than conventional diesel, have more time to mix prior to ignition thus lowing rates of soot formation in these modes. This opens up the possibility of adopting gasoline or fuels with lower cetane numbers within conventional diesel engine technologies.
However, by expanding the number of injections, varying the volume of fuel within each injection event and changing the fuel type, further insight into the impact of these variations must be obtained in terms of their impact on the knock limit and emissions.
THE RESULTS
The srm was used to simulate PPCI combustion
The process of injection, fuel mixing and subsequent auto-ignition were simulated using srm suite. Results were consistent with those observed in the experiments.
Further insight into the sources of emissions
This work has demonstrated that low emissions are observed due to the adoption of high EGR concentrations and optimal injection timings. The figure below highlights how intelligent injection stratagies can be adopted to control the in-cylinder composition such that those regimes expected to generate high rates of soot and NOX formation are avoided.
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