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It has recently been suggested in an experimental study that an aged DOC could be net consumer of engine out NO2 (Katare et al, 2007) thus inhibiting the fast reaction (2NH3 + NO + NO2 => 2N2+3H2O) in an SCR that might follow. Both engine test and flow reactor results indicated that at low temperatures CO and HC reduces NO2 to NO and that CO is much better reductant than HC. The present study investigates the mechanistic story behind this experimentally observed phenomenon by means of a global reaction mechanism. It also investigates the role of CO inhibition of NO oxidation at higher temperature which also plays key role in the overall oxidation efficiency of a DOC. Once a suitable mechanism is defined by comparing against measurements, the current study will use it to examine conditions under which DOC can destroy NO2 and to propose possible strategies to avoid NO2 consumption in order to obtain high SCR efficiency.

Detailed heat transfer measurements were made in the combustion chamber of a Cummins single cylinder NH-engine in two configurations: cooled metal and ceramic-coated. The first configuration served as the baseline for a study of the effects of insulation and wall temperature on heat transfer. The second configuration had several in-cylinder components coated with 1.25 mm (0.050″) layer of zirconia plasma spray -- in particular, piston top, head firedeck and valves. The engine was operated over a matrix of operating points at four engine speeds and several load levels at each speed. The heat flux was measured by thin film thermocouple probes. The data showed that increasing the wall temperature by insulation reduced the heat flux. This reduction was seen both in the peak heat flux value as well as in the time-averaged heat flux. These trends were seen at all of the engine operating conditions.

The use of an optical proximeter to determine dynamic top center in a motored engine is demonstrated. Design criteria are formulated and a data reduction procedure is presented. The method is shown to have an accuracy of Δθ = ± 0.1°. Variations in dynamic top center with engine speed that can be attributed to structural flexing and finite bearing clearances are shown to be less than ± 0.05°. It is also shown that the compression ratio during gas exchange is slightly larger than during compression-expansion. Other methods of finding top center are discussed and contrasted with optical proximetry. In this context a rational means of examining pressure records is presented and shown to be accurate to within Δθ=±0.3°.

A combustion bomb has been developed which allows simulation of diesel combustion without the need to heat the bomb to high temperatures. Simulation of the compression stroke is achieved by burning a lean precharge composed of acetylene, oxygen and nitrogen. By controlling the initial partial pressures of these constituents it is possible to burn them to a state with an oxygen concentration, temperature and pressure representative of conditions in a diesel engine at the start of fuel injection. Diesel fuel injected into these gases autoignites and burns in a manner typical of combustion in diesel engines. This paper describes the design and operation of such a bomb. Experimental results are presented to illustrate its salient features. Particular attention is devoted to various means of obtaining optical access to the flow and the advantages offered over rapid compression machines or heated bombs.