Benefits and Drawbacks of Compression Ratio Reduction in PCCI Combustion Application in an Advanced LD Diesel Engine

<div class="htmlview paragraph">The present paper describes an experimental study on the effect of the compression ratio on the performance of a LD diesel engine operating with a PCCI calibration, near the estimated EURO 6/Tier2 Bin5 NO_x emission limits.</div> <div class="htmlview paragraph">The research activity is the result of a collaborative project between Istituto Motori and Centro Ricerche Fiat aimed to carry out an exhaustive analysis of the compression ratio (CR) influence on the performance of a LD diesel engine. Starting from a reference engine configuration the CR was reduced in two steps sequentially. Each CR value was characterized under PCCI operation mode and, under conventional diesel operating mode, at maximum torque.</div> <div class="htmlview paragraph">The exploration of the PCCI application in the NEDC operating area was performed prefixing limits on maximum fuel consumption, maximum pressure rise and maximum tolerable smoke.</div> <div class="htmlview paragraph">The main result was that no significant increment in PCCI application area reducing the CR was possible without overcoming the limits. But thanks to a drastic drop in smoke emission for the low CR values, a further enlargement of near EURO 6 PCCI application area was possible by means of engine recalibration.</div> <div class="htmlview paragraph">The results allowed the definition of the optimum range values of the CR able to minimize the NO_x-particulate trade-off coupled with acceptable increment in unburned compound emissions (HCs+CO) and FC, helping to the definition of the line-guides for the future EURO 6/Tier2 Bin5 engine design.</div>