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A multi-dimensional combustion code implementing the Conditional Moment Closure turbulent combustion model interfaced with a well-established RANS two-phase flow field solver has been employed to study a broad range of operating conditions for a heavy duty direct-injection common-rail Diesel engine. These conditions include different loads (25%, 50%, 75% and full load) and engine speeds (1250 and 1830 RPM) and, with respect to the fuel path, different injection timings and rail pressures. A total of nine cases have been simulated. Excellent agreement with experimental data has been found for the pressure traces and the heat release rates, without adjusting any model constants. The chemical mechanism used contains a detailed NOx sub-mechanism. The predicted emissions agree reasonably well with the experimental data considering the range of operating points and given no adjustments of any rate constants have been employed.

The presented concept in this study consists of a state of the art passenger car natural-gas engine fired by different hydrogen (H2) and compressed-natural-gas (CNG) fuel blends. The hydrogen content in the fuel was varied among 5 and 15vol% corresponding to 0.6-2.1 mass%, while comparisons include also engine operation on pure CNG. Increasing hydrogen content of the fuel accelerated combustion leading to modest efficiency improvements. Combustion analysis showed that the increasing burning rates mainly affected the initial combustion phase (duration for 5% mass fraction burned). With optimal combinations of spark timing and EGR rate the achievements are additional efficiency increase with substantially lower engine-out NOx while total unburned hydrocarbons or CO-engine-out emissions are not affected. Investigations using Design of Experiments (DoE) algorithms provided a comprehensive picture of the entire parameter space.

In this study, experimental results of homogeneous charge compression ignition HCCI of n-butane in a single shot machine are presented. N-butane measurements are compared with a multizone model. Individual zones are calculated using a perfectly stirred reactor and Chemkin chemistry. The influence of temperature before combustion on heat release rate and duration of combustion is shown in a sensitivity analysis. As a perfect homogeneous temperature and fuel distribution are difficult to establish under experimental conditions, deviations from perfect homogeneity are shown. The influence of a hot surface in the cylinder head in terms of heat release rate and ignitability is examined. Further, dual fuel injections of n-butane and diesel are studied to trigger the n-butane ignition with a defined start of combustion.

Numerical and experimental investigations are presented with regard to homogeneous-charge-compression-ignition for two different fuels. N-heptane and n-butane are considered for covering an appropriate range of ignition behaviour typical for higher hydrocarbons. One fuel is closer to diesel (n-heptane), the other closer to gasoline ignition properties (n-butane). Butane in particular, being gaseous under atmospheric conditions, is used to also guarantee perfectly homogenous mixture composition in the combustion chamber. Starting from detailed chemical mechanisms for both fuels, reaction path analysis is used to derive reduced mechanisms, which are validated in homogeneous reactors. After reduction, reaction kinetics is coupled with multi zone modeling and 3D-CFD through the Conditional Moment Closure (CMC) approach in order to predict autoignition and heat release rates in an I.C. engine. Multi zone modeling is used to simulate port injection HCCI technology with n-butane.

The premixed flame growth period of about 1% of the cylinder mass burned has been theoretically investigated under typical homogeneous charge engine conditions. For this purpose various flame kernel development models have been tested against measured values of flame radius vs. time after ignition in a research engine. The flame kernel growth has been computed on the basis of a zero-dimensional model incorporating spark-induced energy, heat loss to the electrodes and flame curvature effects. Subsequently the transition phase from laminar to fully turbulent flame propagation is shown to depend strongly on the relationship between the turbulent kinetic energy spectrum and characteristic scales of the flame. We thereby make use of recently reported results of fundamental experiments on vortex-flamelet interaction, that yield typical vortex sizes for flame wrinkling and quenching.

Measurements of instantaneous in-cylinder heat transfer have been performed at a selected location of the cylinder head in a super long stroke, low speed, two-stroke experimental diesel engine operating under various conditions. The temperatures of both the wall and the process have been varied either by locally using titanium instead of steel as wall material or correspondingly by operating the engine with an unusually high equivalence ratio. A standard case with a steel wall and a typical full load point has been used as reference. For all conditions, measurements of the wall temperature very close to the surface of the apparent radiation temperature of the combustion chamber contents and of the gas temperature across the boundary layer (the latter by means of a for this purpose specifically developed fiber-optical sensor) have been carried out. As a result, the total heat flux as well as its two components, convection and radiation, have been determined.