Miller cycle for improved efficiency, load range and emissions in a heavy-duty engine running under reactivity controlled compression ignition combustion

Abstract

The low temperature, premixed combustion strategies are being investigated in the recent years as a mean to break the NOx-soot trade-off appearing during the diffusive conventional diesel combustion. This approach relies on promoting premixed combustion events with shortened duration, which reduces the heat transfer losses, improves the thermal efficiency, and allows a simultaneous reduction of engine-out NOx and soot emissions. However, since the combustion onset only depends on chemical kinetics, most of these strategies cannot be implemented at medium and high loads due to excessive pressure gradients, which lead to unacceptable noise levels and reliability issues. This experimental work investigates the potential of the Miller cycle as a strategy to minimize the aforementioned challenges when operating under reactivity controlled compression ignition combustion. Moreover, the coupled effect of the Miller cycle with the fuel reactivity modulation is also explored as a way for improving the combustion control. For this purpose, parametric studies varying the effective compression ratio and gasoline fraction have been done in a single-cylinder heavy-duty engine operating at 14 bar indicated mean effective pressure and 1200 rev/min as a baseline condition. The results show that this strategy allows better control of the in-cylinder thermodynamic conditions, enabling a simultaneous reduction of nitrogen oxides and soot emissions down to the EURO VI limits, while keeping a reduced fuel consumption and suitable incylinder maximum pressure gradients.

Comparison of the Diffusive Flame Structure for Dodecane and OME _X Fuels for Conditions of Spray A of the ECN

“…In this regard, the advanced combustion modes such as low temperature combustion (LTC) are considered as promising ways to reduce NOX and soot emissions whilst keeping high combustion efficiency [2,3], which could contribute to the simplification of the aftertreatment devices. The use of high exhaust gas recirculation rates (EGR) combined with more premixed conditions than in conventional diesel combustion allow achieving extremely low soot and NOX emissions [4]. Even potentially better emission reductions can be obtained with other strategies such as dual fuel dual mode combustion or Reactivity controlled compression ignition (RCCI) in compression ignition engines in the whole combustion map operating range as recently shown in [5].…”

Miller cycle combined with exhaust gas recirculation and post–fuel injection for emissions and exhaust gas temperature control of a heavy-duty diesel engine

“…17–19 In recent years, however, the main research focus has been on the reduction of NOx emissions from on-road diesel vehicles as the emissions regulation become increasingly stringent. 20–24…”

Performance and emissions of a series hybrid vehicle powered by a gasoline partially premixed combustion engine

“…The basis of this combustion mode has its roots in the work by Inagaki et al [14], where they proposed a dual-fuel premixed compression ignition (PCI) combustion strategy using two fuels with different reactivity. In this concept, the fuels are injected into the cylinder using two separate injection systems, allowing the variation of each fuel independently according to the engine operating conditions [15]. By means of experimental tests, the authors confirmed better combustion controllability than HCCI with low NOx and soot emissions.…”