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Soot formation and oxidation are complex and competing processes during diesel combustion. The balance between the two processes and their history determines engine-out soot values. Besides the efforts to lower soot formation with measures to influence the flame lift-off distance for example or to use HCCI-combustion, enhancement of late soot oxidation is of equal importance for low-λ diffusion-controlled low emissions combustion with EGR. The purpose of this study is to investigate soot oxidation in a heavy duty diesel engine by statistical analysis of engine data and in-cylinder endoscopic high speed photography together with CFD simulations with a main focus on large scale in-cylinder gas motion. Results from CFD simulations using a detailed soot model were used to reveal details about the soot oxidation.

A validation study of the numerical model of n-heptane spray combustion based on experimental constant-volume data [1] was done, by comparing auto-ignition delays for different pre - turbulence levels and initial temperatures, flame contours, and soot distributions under Diesel-like conditions. The basic novelty of the methodology developed in [2] - [3] is the implementation of the partially stirred reactor (PaSR) model accounting for detailed chemistry / turbulence interactions. It is based on the assumption that the chemical processes proceed in two successive steps: micro mixing, simulated on a sub - grid scale, is followed by the reaction act. When the all Re number RNG k-ε or LES models are employed, the micro mixing time can be consistently defined giving the combustion model a “well-closed” form incorporated into the KIVA-3V code.

A system for stratifying recycled exhaust gas (EGR) to substantially increase dilution tolerance has been applied to a multi-cylinder port injected four-valve gasoline engine. This system, dubbed Combustion Control through Vortex Stratification (CCVS), has shown greatly improved fuel consumption at stoichiometric conditions whilst retaining ULEV compatible engine-out NOx and HC emission levels. A production feasible variable air motion system has also been assessed which enables stratification at part load with no loss of performance or refinement at full load.

Fuel wetting in the inlet port of a gasoline engine was studied using Laser-Induced Fluorescence (LIF). The measurements were done directly on the metal wall surface. Quantitative results were be obtained using a special calibration procedure. The sensitivity of the technique was found to correspond to a fuel layer thickness in the order of 1 μm, and the accuracy was estimated to be approx. 10 %. The engine was run on iso-octane, and in order to obtain fluorescence a dopant (3-pentanone) was added to the fuel. Laser light with a wave length of 266 nm was generated by frequency doubling the light from a Nd-YAG laser in two steps. A laser sheet was directed into the intake port and the fuel layer on the wall could be studied along a line on the bifurcation wall. The fluorescence light was detected with an intensified diode-array camera. The measurements from the fuel film thickness were compared with measurements of the total fuel film mass using an A/F response method.

The compression ratio is an important engine design parameter. It determines to a large extend engine properties like the achievable efficiency, the heat losses from the combustion chamber and the exhaust losses. The same properties are affected by insulation of the combustion chamber. It is therefore especially important to know the compression ratio when doing experiments with thermal barrier coatings (TBC). In case of porous TBCs, the standard methods to measure the compression ratio can give wrong results. When measuring the compression ratio by volume, using a liquid, it is uncertain if the liquid fills the total porous volume of the coating. And for a thermodynamic compression ratio estimation, a model for the heat losses is needed, which is not available when doing experiments with insulation. The subject of this paper is the evaluation of an alternative method to assess the compression ratio.