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The effect of three oxidation catalysts (Honeycat DEP 290, Engelhard PTX 623, Herapur 20L) and one catalytic trap oxidizer (Johnson Matthey JM 13/II) on the emissions of a RABA (M.A.N. Licensed) heavy-duty diesel engine has been comparatively studied. Tests were conducted according to EPA 13 mode test to measure CO, total HC, NOx and total particulate matter emitted by the engine with and without devices. The test results were also correlated to the total emissions of the Athenian buses through new weighing factors of an “Athenian 13 mode test”. The engine tests for all four devices resulted in: (1) considerable reduction of the engines CO and total HC emissions - being already low (2) practicaly no difference in NOx emissions and (3) increase of the total particulate emissions at high load modes.

The paper presents a mathematical model for the simulation of the operational characteristics of the trap during transient operation, based on trap inlet conditions of the exhaust gas and trap history. The model incorporates (a) the formulation of flow conditions in the trap (b) the fundamental mass and energy balance of the system (c) the formulation of the oxidation process through chemical kinetics and (d) the description of mass and heat transfer conditions, including the possibility for calculation of trap operation during both particulate accumulation and regeneration phases. The major output of the model comprises ceramic wall and exhaust gas temperature fields in the trap, as functions of time, as well as the loading level of the trap. The application of the simulation model clarifies the critical importance of the wall temperature at trap outlet and forecasts the failure probability of the ceramic material due to overheating, under specific conditions at trap inlet.

A regeneration system for the ceramic trap oxidiser is presented, based on the exhaust gas throttling of the engine. The trottling process, producing 1.5-3.0 bar overpressure, leads to a modified power flow in the engine, resulting in higher enthalpy exhaust gas, at the expense of the net power output of the engine. Thus exhaust temperature is raised over the lower regeneration limit (550°C) for a wide range of engine operation modes including also high speed-no-load modes. The effects of throttling on exhaust gas thermodynamic state and engine operational characteristics (volumetric efficiency, mean effective pressure, power output, consumption) are theoretically and experimentally analysed. An optimised regeneration system by exhaust throttling is described. This system includes: regulated throttling orifice for minimum net power output loss and reduction of fuel injected for acceptable smoke emission of the engine under high backpressure conditions.

A method for the determination of the size of the ceramic trap according to the engine and its use, has been developed. The calculation algorithm is presented, based on fundamental considerations concerning trap operation during regeneration and accumulation, and taking into account the parameters imposed by the engine. The application of the method is then presented, with the example of engines from within the range of 30-300 kW rated power. A module configuration of the trap oxidiser consisting of a number of Corning EX 47, 5.66″ × 6″ filter elements is used.

The oxidizing behavior of the ceramic diesel particulate trap Corning EX 47 is examined under forced regeneration by exhaust gas throttling, based on a trap loading model, assuming soot accumulation from channel outlet towards inlet. The required conditions which may lead to an extended life of the trap are investigated. It is deduced that regeneration of a trap, even totally loaded, is possible, provided that exhaust temperature does not exceed 650°C and mass flow through the trap is higher than a lower critical value.