Simulations of Compression Ignition Engines with Detailed Chemistry and Spray Models

Internal combustion engines (ICEs) have been the preferred power train for both light and heavy-duty applications due to its high efficiency and power output, good fuel economy, and low engine noise. During the past decade the ICE technology has seen significant advances such as high pressure injection, low-temperature combustion, and flexibility to run variety of bio-derived fuels. ICEs are characterized by turbulence, multi-phase flows, and complicated (not well understood) spray physics. Furthermore, turbulence-chemistry interactions, moving boundaries (piston and valves), heat-transfer (conduction, convection, and radiation), and complex combustion chemistry of fuel oxidation and emission formation make predictive engine simulations a computationally daunting task. This talk will specifically focus on developing and validating spray and combustion models for bio-derived fuels such as soy-derived biodiesel.

In an ICE (diesel engine) the liquid fuel is injected into the combustion chamber near the end of the compression stroke. Following injection, the fuel undergoes atomization and vaporization processes, followed by fuel-air mixing, ignition, and establishment of a lifted flame in the chamber. These spray and combustion processes are highly coupled in nature. The first part of the talk will focus on demonstrating that the spray model developed can accurately predict the liquid fuel distribution in the combustion chamber. Combustion modeling with biodiesel will be performed using a surrogate mixture of methyl butanoate and n-heptane. The detailed model developed in-house is first reduced for ICE simulations. This reduced chemical kinetic model is used to predict the ignition delay, flame lift-off length, pressure trace, heat release rate, and emission characteristics of soy-derived biodiesel in a single-cylinder Caterpillar Inc. research engine at Argonne National Laboratory. Parametric studies will be shown demonstrating the influence of injection and ambient conditions on performance and emission characteristics of the ICE. Following the validation process, the influence of uncertainty in measurement of the rate coefficients on ignition delay and species evolution profile will be presented. Recommendations will be made regarding important reactions of interest for ICE simulations and the pressure, temperature, and equivalence ratio conditions under which these reactions occur.

These developments in the field of spray and combustion modeling are important steps towards predictive simulations of the ICEs operating on a large variety of fuels.