Dual fuel low temperature combustion (LTC) strategies are attractive for future internal combustion engines due to their promise of very low engine-out emissions of oxides of nitrogen (NO x) and particulate matter. In the present work, experimental results for diesel-ignited methane dual fuel LTC on a compression ignition single cylinder research engine (SCRE) are presented. Methane was fumigated into the intake manifold and diesel injection was used to initiate combustion. The engine was operated at a constant speed of 1500 rev/min, and diesel injection pressure was fixed at 500 bar. The start of injection (SOI) of diesel fuel was varied from 260º to 360º (i.e., TDC) to quantify its impact on engine performance and engine-out, indicated-specific emissions of NO x (ISNO x), carbon monoxide (ISCO), and unburned hydrocarbons (ISHC), and smoke emissions. The SOI sweeps were performed at different net indicated mean effective pressures (IMEPs) of 4.1 and 12.1 bar. Intake manifold pressure and methane percent energy substitution (PES) were fixed at 1.5 bar and 80%, respectively, for 4.1 bar IMEP and at 1.8 bar and 95%, respectively, for 12.1 bar IMEP. For all loads, when SOI was advanced, the longer ignition delays caused the separation between the fuel injection and the combustion events to increase. This was accompanied by a change in the shape of the AHRR curve from a distinct two-stage profile to a smooth, single-stage (almost Gaussian) profile.
Diesel-ignited propane dual fuel low temperature combustion was characterized in a singlecylinder research engine (SCRE) at constant values of indicated mean effective pressure (IMEP of 5.1 bar), engine speed (1500 rpm), and propane energy substitution (PES = 80%). The effects of three important engine parameters (start of injection (SOI) of diesel fuel, common-rail pressure (Prail) for diesel injection, and boost pressure (Pin)) on engine performance, combustion, and emissions were examined. As SOI was advanced from 355 absolute crank angle degrees (CAD) (or 5° BTDC) to 280 CAD for constant Prail = 500 bar and Pin = 1.5 bar, the apparent heat release rate (AHRR) profiles changed from a two-stage, "diesel-like" combustion process to a smooth, "Gaussian-like," single-stage combustion process, that was representative of more homogeneous combustion. In addition, with SOI advancement, the combustion phasing (CA50) was initially advanced but eventually occurred later for very early SOIs. Indicated-specific emissions of oxides of nitrogen (ISNOx) were reduced to about 0.12 g/kWh for SOIs advanced beyond 310 CAD while maintaining high indicated fuel conversion efficiencies (IFCEs). While smoke emissions were below 0.1 FSN for all conditions tested in this study, indicated-specific hydrocarbon (ISHC) and
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