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Non-homogeneities in the exhaust line regarding flow distribution and mixing of exhaust gases upstream of catalytic converters or particulate filters are a major source of conversion efficiency reduction due to partial volume utilization. Current supports for catalytic converters use a honeycomb monolithic substrate with only a limited potential for increased wall contacts of the gas molecules due to their laminar channel flow profile. Non homogeneities of the flow distribution at the entering cross section of the catalytic converter prevail also inside the converter channels since no momentum exchange is possible perpendicular to the main flow direction. The ceramic based foams developed and patented by Empa are a promising alternative. In the upstream of exhaust aftertreatment devices they ceramic foams redistribute the exhaust gases homogenizing the flow, enhancing turbulence and species mixing, without increasing flow resistance to prohibitive levels.

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.

Tailpipe particle measurements have been performed in Euro-4 passenger cars. The investigation included compressed natural gas fuelled (bifuel vehicle concepts, commercially available) spark-ignition vehicles, gasoline port-injection spark-ignition vehicles, gasoline direct injection spark-ignition vehicles as well as compression ignited, diesel vehicles with and without particle filters. Particle number and soot mass was measured. In addition particle number size distributions have been recorded at constant vehicle speed operation. In the current study, the particle emissions of Compressed Natural Gas (CNG) vehicles are significantly lower than the corresponding ones of the other spark-ignition vehicles.

The optimisation of the operating parameters optimisation for the IVECO small, high speed, turbocharged, DI Diesel engine for reaching Euro 3 emission levels, has been performed using statistical methods. The engine is equipped with a Common Rail injection system and some market versions are also equipped with a variable geometry turbocharger (VGT) as well as/or electronically controlled exhaust gas recirculation (EGR), hence, there are numerous operating parameters to be taken into account during mapping. The injection systems flexibility is very high. It allows independent injection pressures and timings as well as multiple injection throughout the entire engine map. Variable geometry turbochargers (VGT) enable the control of the optimal boost pressure. Finally consideration of exhaust gas recirculation (EGR) provides one more independent parameter to deal with.

Coincident 3-d velocity measurements in the flat combustion chamber of a motored single cylinder engine have been performed using Laser-Doppler-Velocimetry. The 3-d LDV System consisted of three beampairs (514nm, 488nm and 476.5nm) and two fiberoptic probes operated in 90° cross-scatter mode obtaining high spatial and temporal resolution as well as high signal quality. Burst Spectrum Analyzers have been thereby used for signal processing. The time histories of the three velocity components have been acquired for moderate engine speeds (600, 1000 and 1500RPM). The swirling motion in the cylinder was also varied by choosing different fixed positions of a shrouded intake valve relative to the intake port. Several measuring locations in the combustion chamber have been studied in order to investigate homogeneity. Mean velocities and fluctuation intensities of the turbulent field were evaluated using ensemble averaging.

Coincident 3-D velocity measurements have been made in a single-cylinder, motored research engine using a six-beam, three-wavelength LDV system. The engine had a pancake combustion chamber, a compression ratio of 8.0 and was operated with a fixed intake shroud valve position. Measurements have been performed at 600, 1000 and 1500 RPM and at three distinct locations within the combustion chamber. Software coincidence filtering and ensemble averaging have been thereby used for data processing.

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.