Search Results

A set of reduced chemical mechanisms was developed for use in multi-dimensional engine simulations of premixed gasoline combustion. The detailed Primary Reference Fuel (PRF) mechanism (1034 species, 4236 reactions) from Lawrence Livermore National Laboratory (LLNL) was employed as the starting mechanism. The detailed mechanism, referred to here as LLNL-PRF, was reduced using a technique known as Parallel Direct Relation Graph with Error Propagation and Sensitivity Analysis. This technique allows for efficient mechanism reduction by parallelizing the ignition delay calculations used in the reduction process. The reduction was performed for a temperature range of 800 to 1500 K and equivalence ratios of 0.5 to 1.5. The pressure range of interest was 0.75 bar to 40 bar, as dictated by the wide range in spark timing cylinder pressures for the various cases. In order to keep the mechanisms relatively small, two reductions were performed.

EGR systems are widely applied in modern turbocharged diesel engines to reduce engine-out emissions and will, or are being used to mitigate engine knock in SI engines for improved SI engine efficiency and power. In this paper, different EGR systems are detailed and evaluated theoretically based on the thermodynamics of a turbocharged system featuring an EGR sub-system. Turbine expansion ratio is utilized as a metric to estimate engine efficiency, i.e., pumping losses during the gas exchange process. Approaches such as compressor and turbine bypassing are evaluated as well. Based on above analysis, a new approach is put forward to expand the turbocharger work zone, particularly in the high efficiency regions by correctly utilizing EGR systems at all engine speed range: low-pressure loop EGR system at lower engine speed range and high-pressure loop EGR system at high engine speed range.