Investigation of the effects of split-injection on particle emissions from a Dieseline CI engine

Premixed compression ignition (PCI) combustion techniques utilising low cetane-number (<40) fuels are associated with low engine-out oxides of nitrogen (NOx) and soot emissions. However, fuel-air over-mixing and high combustion noise at low and high engine loads, respectively, have been the challenges with PCI. Fuel split-injection can effectively govern the fuel-air mixing process and subsequently control combustion and emissions characteristics; it is of interest to characterise particle emissions under these PCI conditions. In this study, the effects of double-injection of low-cetane G75-Dieseline (75% gasoline in diesel based on volume) on controlling charge premixing and consequently size distribution of particle emissions were investigated in a production light-duty 4-cylinder CI engine. First injection-quantity ratio was varied from 10% to 50% while using different injection timings at engine loads from 1.4 to 12 bar BMEP and speed of 1800 RPM. Brake specific emissions results were compared to diesel baselines to quantify particles concentration reduction while maintaining the same range of NOx and brake thermal efficiency (BTE). G75 combustion emitted lower number and mass of particles (in all size classes) by up to 99.9% and generally lower NOx by up to 65% compared to diesel. Negligible particle number and mass emissions (as low as 1.91 × 1012 parts/kWh and 138 µg/kWh respectively) were measured for G75 at low-medium loads (3–6 bar BMEP). In the absence of two-stage combustion, the timing of second-injection controlled the combustion-phasing effectively. Lower first injection-quantity ratios (e.g. 10%) are recommended for overall high BTE and low gaseous and particle emissions.