Search Results

A new metal foam material for diesel particulate filtration, trademarked as INCOFOAM® HighTemp, was recently presented. Extensive tests showed the potential of achieving filtration efficiencies of the order of 85% or more at low pressure drop using a radial flow design concept with graded foam porosity. By applying a catalytic washcoat, the foam exhibits enhanced gas mixing and thus higher conversion efficiencies at high space velocities. In addition, due to an excellent soot-catalyst contact, the washcoated foam exhibited high catalytic regeneration rates. The present paper focuses on a novel “cross-flow” design concept for a better filtration/pressure drop trade-off as well as application of the foam as an oxidation catalyst substrate. The experimental testing starts from small-scale reactors and proceeds to real exhaust testing on the engine bench as well as vehicle tests on the chassis dynamometer and on-road testing.

The objective of this study is to present a particulate filter concept, based on a new porous material: INCOFOAM® HighTemp, a Ni-based superalloy foam. The paper examines the filtration and pressure drop characteristics as well as the regeneration performance of different filter configurations, based on experimental data and modeling. A number of different foam structures with variable pore characteristics are studied. The experimental testing covers flow and pressure drop behavior with air and exhaust gas, filtration efficiency measurements as function of particle size and regeneration rate measurements. The testing starts from mini-scale reactors and proceeds to real exhaust testing on the engine bench as well as vehicle tests on the chassis dynamometer and on-road. In parallel, a previously developed mathematical model is applied to study and understand the filtration and pressure drop mechanisms in the case of clean and soot loaded filters.

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.

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.