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Experimental data and modeling work have shown that gasoline-like fuels can potentially be used to simultaneously achieve high efficiency and low pollutant emissions in compression ignition engines. Demonstrating that existing hardware systems are tolerant to these fuels is a key step in harnessing this potential. In this study, a 400-hour North Atlantic Treaty Organization (NATO) test cycle was used to assess the overall robustness of a Cummins XPI common-rail injection system operating with gasoline-like fuel. The cycle was designed to accelerate wear and identify any significant failure modes that could appear under normal operating conditions. Although prior work has investigated injection system durability with a wide variety of alternative fuels, this study uniquely focuses on a high-volatility, low-viscosity, gasoline-like fuel that has been dosed with lubricity additive.

Cyclic variability in internal combustion engines (ICEs) arises from multiple concurrent sources, many of which remain to be fully understood and controlled. This variability can, in turn, affect the behavior of the engine resulting in undesirable deviations from the expected operating conditions and performance. Shot-to-shot variation during the fuel injection process is strongly suspected of being a source of cyclic variability. This study focuses on the shot-to-shot variability of injector needle motion and its influence on the internal nozzle flow behavior using diesel fuel. High-speed x-ray imaging techniques have been used to extract high-resolution injector geometry images of the sac, orifices, and needle tip that allowed the true dynamics of the needle motion to emerge. These measurements showed high repeatability in the needle lift profile across multiple injection events, while the needle radial displacement was characterized by a much higher degree of randomness.

Synchrotron x-radiography and a novel fast x-ray detector are used to visualize the detailed, time-resolved structure of the fluid jets generated by a high pressure diesel-fuel injection. An understanding of the structure of the high-pressure spray is important in optimizing the injection process to increase fuel efficiency and reduce pollutants. It is shown that x-radiography can provide a quantitative measure of the mass distribution of the fuel. Such analysis has been impossible with optical imaging due to the multiple-scattering of visible light by small atomized fuel droplets surrounding the jet. In addition, direct visualization of the jet-induced shock wave proves that the fuel jets become supersonic under appropriate injection conditions. The radiographic images also allow quantitative analysis of the thermodynamic properties of the shock wave.

The efficiency and emission potential of pre-chamber combustion in a Miller cycle light duty gasoline engine operated under part load was evaluated. Several pre-chamber designs that examine the engine performance tradeoffs with nozzle diameter, pre-chamber volume, number of nozzles, and pre-chamber fuel enrichment were investigated for both excess air and cooled external EGR dilution strategies. The introduction of pre-chamber jet ignition was observed to significantly reduce the main-chamber combustion duration while reducing cyclic variability under dilute conditions, benefiting from the long-reach ignition jets and enhanced turbulence. However, the pre-chamber design that provided the fastest combustion led to reduced brake efficiency primarily due to increased wall heat loss. Maintaining the total nozzle area while increasing the number of nozzles was identified as a means to minimize the additional heat loss and maintain fast burn rates.