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Low-Speed pre-ignition (LSPI) in modern-day, heavily downsized, boosted, and direct-injection spark ignition (SI) engines is a well-known problem. Several mechanisms contribute towards stochastic pre-ignition (SPI), the most prominent being crevice material droplet induced and deposit induced pre-ignition mechanisms. The droplet mechanism is typically dominated by the detergent additives present in the lubricant formulation; more specifically calcium and sodium-based detergent additives correlate strongly with the increased LSPI rates. Deposits flaking off the combustion chamber surfaces can also induce LSPI under certain conditions. This study aimed to develop an optical method designed to investigate the nature of pre-ignition precursors. Southwest Research Institute (SwRI) utilized an optically accessible GM 2.0 L LHU engine to study the pre-ignition phenomenon and studied the nature of pre-ignition precursors using spectral information from one of the cylinders in this engine.

Numerous studies have characterized the impact of high injection pressure and small nozzle holes on spray quality and the subsequent impact on combustion. Higher injection pressure or smaller nozzle diameter usually reduce soot emissions owing to better atomization quality and fuel-air mixing enhancement. The influence of nozzle geometry on spray and combustion of diesel continues to be a topic of great research interest. An alternate approach impacting spray quality is investigated in this paper, specifically the impact of non-circular nozzles. The concept was explored experimentally in an optically accessible constant-volume combustion chamber (CVCC). Non-reacting spray evaluations were conducted at various ambient densities (14.8, 22.8, 30 kg/m3) under inert gas of Nitrogen (N2) while injection pressure was kept at 100 MPa. Shadowgraph imaging was used to obtain macroscopic spray characteristics such as spray structure, spray penetration, and the spray cone angle.

The influence of nozzle geometry on spray and combustion of diesel continues to be a topic of great research interest. One area of promise, injector nozzles with micro-holes (i.e. down to 30 μm), still need further investigation. Reduction of nozzle orifice diameter and increased fuel injection pressure typically promotes air entrainment near-nozzle during start of injection. This leads to better premixing and consequently leaner combustion, hence lowering the formation of soot. Advances in numerical simulation have made it possible to study the effect of different nozzle diameters on the spray and combustion in great detail. In this study, a baseline model was developed for investigating the spray and combustion of diesel fuel at the Spray A condition (nozzle diameter of 90 μm) from the Engine Combustion Network (ECN) community.