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Technical Paper

Large Eddy Simulation of an Ignition Front in a Heavy Duty Partially Premixed Combustion Engine

In partially premixed combustion engines high octane number fuels are injected into the cylinder during the late part of the compression cycle, giving the fuel and oxidizer enough time to mix into a desirable stratified mixture. If ignited by auto-ignition such a gas composition can react in a combustion mode dominated by ignition wave propagation. 3D-CFD modeling of such a combustion mode is challenging as the rate of fuel consumption can be dependent on both mixing history and turbulence acting on the reaction wave. This paper presents a large eddy simulation (LES) study of the effects of stratification in scalar concentration (enthalpy and reactant mass fraction) due to large scale turbulence on the propagation of reaction waves in PPC combustion engines. The studied case is a closed cycle simulation of a single cylinder of a Scania D13 engine running PRF81 (81% iso-octane and 19% n-heptane).
Technical Paper

A Coupled Tabulated Kinetics and Flame Propagation Model for the Simulation of Fumigated Medium Speed Dual-Fuel Engines

The present work describes the numerical modeling of medium-speed marine engines, operating in a fumigated dual-fuel mode, i.e. with the second fuel injected in the ports. This engine technology allows reducing engine-out emissions while maintaining the engine efficiency and can be fairly easily retrofitted from current diesel engines. The main premixed fuel that is added can be a low-carbon one and can additionally be of a renewable nature, thereby reducing or even completely removing the global warming impact. To fully optimize the operational parameters of such a large marine engine, computational fluid dynamics can be very helpful. Accurately describing the combustion process in such an engine is key, as the prediction of the heat release and the pollutant formation is crucial. Auto-ignition of the diesel fuel needs to be captured, followed by the combustion and flame propagation of the premixed fuel.
Technical Paper

Effect of Injection Timing on the Ignition and Mode of Combustion in a HD PPC Engine Running Low Load

This work aims to study the effect of fuel inhomogeneity on the ignition process and subsequent combustion in a compression ignition Partially Premixed Combustion (PPC) engine using a primary reference fuel (PRF) in low load conditions. Five cases with injection timings ranging from the start of injection (SOI) at -70 crank angle degrees (CAD) to -17 CAD have been studied numerically and experimentally in a heavy duty (HD) piston bowl geometry. Intake temperature is adjusted to keep the combustion phasing constant. Three dimensional numerical simulations are performed in a closed cycle sector domain using the Reynolds Averaged Navier-Stokes (RANS) formulation with k-ϵ turbulence closure and direct coupling of finite rate chemistry. The results are compared with engine experiments. The predicted trends in required intake temperature and auto-ignition location for a constant combustion phasing are consistent with experiments.
Technical Paper

CFD Study of Low Soot Spray Combustionin a Heavy-Duty Diesel Engine

This CFD study focuses on the influence of the nozzle diameter on the mixing process and the soot formation and oxidation process in a heavy-duty diesel engine. The CFD simulation is based on the Reynolds Averaged Navier-Stokes approach. The engine set-up is similar to an experimental case that showed rather low soot emission. The aim of the paper is to improve the understanding of the physics of the mixing process in a real engine environment with the attention to scrutinize its effect of fuel injection on combustion and soot emission. Two non-reacting cases with different injector nozzle diameters but constant injection pressure and their corresponding reacting cases are simulated with dynamic mesh motion and fuel spray modeling. The influence of injections on the mixing, combustion and emissions is analyzed and the simulation results are compared with the measurement data.
Technical Paper

Numerical Estimation of Asymmetry of In-Cylinder Flow in a Light Duty Direct Injection Engine with Re-Entrant Piston Bowl

Partially premixed combustion (PPC) can be applied to decrease emissions and increase fuel efficiency in direct injection, compression ignition (DICI) combustion engines. PPC is strongly influenced by the mixing of fuel and oxidizer, which for a given fuel is controlled mainly by (a) the fuel injection, (b) the in-cylinder flow, and (c) the geometry and dynamics of the engine. As the injection timings can vary over a wide range in PPC combustion, detailed knowledge of the in-cylinder flow over the whole intake and compression strokes can improve our understanding of PPC combustion. In computational fluid dynamics (CFD) the in-cylinder flow is sometimes simplified and modeled as a solid-body rotation profile at some time prior to injection to produce a realistic flow field at the moment of injection. In real engines, the in-cylinder flow motion is governed by the intake manifold, the valve motion, and the engine geometry.