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The aim of this study is to see how geometry generated turbulence affects the Rate of Heat Release (ROHR) in an HCCI engine. HCCI combustion is limited in load due to high peak pressures and too fast combustion. If the speed of combustion can be decreased the load range can be extended. Therefore two different combustion chamber geometries were investigated, one with a disc shape and one with a square bowl in piston. The later one provokes squish-generated gas flow into the bowl causing turbulence. The disc shaped combustion chamber was used as a reference case. Combustion duration and ROHR were studied using heat release analysis. A Scania D12 Diesel engine, converted to port injected HCCI with ethanol was used for the experiments. An engine speed of 1200 rpm was applied throughout the tests. The effect of air/fuel ratio and combustion phasing was also studied.

The Homogeneous Charge Compression Ignition (HCCI) combustion progress has been characterized by means of high-speed fuel tracer Planar Laser Induced Fluorescence (PLIF) combined with simultaneous chemiluminescence imaging. Imaging has been conducted using a high-speed laser and detector system. The system can acquire a sequence of eight images within less than one crank angle. The engine was run at 1200 rpm on iso-octane or ethanol and a slight amount of acetone was added as a fuel tracer, providing a marker for the unburned areas. The PLIF sequences showed that, during the first stage of combustion, a well distributed decay of fuel concentration occurs. During the later parts of the combustion process the fuel concentration images present much more structure, with distinct edges between islands of unburned fuel and products.

In this paper, the formaldehyde emissions from three different types of homogenous charge compression ignition (HCCI) engines are quantified for a range of fuels by means of Fourier Transform Infra Red (FTIR) spectroscopic analysis. The engines types are differentiated in the way the charge is prepared. The characterized engines are; the conventional port fuel injected one, a type that traps residuals by means of a Negative Valve Overlap (NVO) and finally a Direct Injected (DI) one. Fuels ranging from pure n-heptane to iso-octane via diesel, gasoline, PRF80, methanol and ethanol were characterized. Generally, the amount of formaldehyde found in the exhaust was decreasing with decreasing air/fuel ratio, advanced timing and increasing cycle temperature. It was found that increasing the source of formaldehyde i.e. the ratio of heat released in the cool-flame, brought on higher exhaust contents of formaldehyde.