No abstract

Understanding of the mechanisms that a ect ow and pressure drop in porous ceramic diesel particulate lters is important in the design optimization of this class of diesel exhaust aftertreatment systems. Furthermore, determination of the parameters involved in the calculation of pressure drop as a function of collected soot mass is important for successful lter loading and regeneration modelling. This paper presents the results of an experimental analysis of pressure drop as a function of the geometric and operating parameters of cordierite and SiC diesel lters. Singlecell lters from cordierite and silicon carbide were prepared to single out any e ects from the complex ow processes that take place in a full-sized lter. The product of soot layer permeability and density was experimentally determined by employing a specially designed experimental apparatus. The calculation was supported by a simple computer calculation that is also presented in this paper. The distribution of soot loading inside the channels of a full-sized lter, in various loaded and partially regenerated conditions, was assessed by connecting the apparatus to discharge through selected channels of the lter. The results are shown to improve understanding of the e ects of partial regeneration and fuel additive residuals on lter back pressure and ow and soot loading distribution. Keywords: diesel particulate lters, pressure drop, ow maldistribution, diesel soot permeability, regeneration, fuel additives T 0 stagnation temperature ( K ) NOTATION u velocity (m/s) U mean ltration velocity (m/s) A area (m2) V vessel volume (m3) C D discharge coe cient w single-channel lter width (m) dm i mass discharged at the ith time step (kg/s) E substrate thickness (m) c speci c heat ratio c p /c v k permeability (m2) ¢P pressure drop across a single-channel lter L single-channel lter length (m) (Pa) m mass ( kg) (¢P) c calculated pressure drop across a single m v mass of air present in the vessel (kg) channel (Pa) m Ç real real mass owrate ( kg/s) m dynamic viscosity (Pa s) Ma Mach number r density (kg/m3) p T throat pressure ( Pa) (rk) p soot layer density times permeability product p Tc calculated pressure in the throat (Pa) (kg/m) p TG guessed pressure in the throat (Pa) p 0 vessel (identical to stagnation) pressure (Pa) R ideal gas constant [R air =287 kJ/(kg K )] Subscripts t time (s) atm atmospheric T temperature ( K ) c calculated ch channel f lter The MS was

Understanding the flow maldistribution phenomena inside porous ceramic diesel particulate filters and their effects on the pressure drop and regeneration characteristics is important for the successful design and modelling of this class of exhaust aftertreatment system. In this paper the results from an experimental study of flow distribution in wall-flow diesel filters are presented. The experiments were performed on a specially designed cold flow test rig, under steady state flow conditions. The flow distribution at the exit of cordierite and SiC filters were measured with a hot film velocity sensor under low and medium mass flowrate conditions. The system configuration was varied to incorporate tests with and without the installation of an oxidation catalyst before the filter in order to investigate the effect of the catalyst honeycomb structure to the measured flow distribution. Flow distribution in filters loaded with various levels of particulate mass was also measured using the same device. The filters were loaded in a modern diesel engine run on catalyst-doped fuel up to different backpressure levels. A flow uniformity index was adopted in order to quantify the measured flow maldistribution by a single number for each case. The velocity distribution at the exit of the filters is found to be significantly affected by certain design and operating parameters of the system: diffuser-catalyst-filter. The results of this work aim to give a better assessment of the magnitude of flow maldistribution in diesel filters, which severely distort their pressure drop characteristics and affect the distribution of collected soot mass. In this way, a previously neglected aspect of the complex three-dimensional filter regeneration behaviour is better understood.

The study of catalytic regeneration characteristics of porous ceramic diesel particulate lters (DPFs) is of growing interest to industry as diesel soot emissions are limited by legislation to levels below 0.01 g/km (for passenger cars). More speci cally, pressure drop computations and correlations are important factors employed in the design and control of diesel lter systems. However, in numerous cases, computations and models fail to match the experimentally observed evolution of soot combustion in the lter. In this paper, the role of ow maldistribution in this issue is investigated, by means of full-scale tests of the loading and regeneration behaviour of a particulate lter installed on a modern diesel engine run on catalyst-doped fuel. Loading tests were performed at three characteristic engine operation points with markedly di erent levels of engine exhaust gas mass owrate. In these tests, it becomes apparent that complex ow maldistribution phenomena exist during the loading phase, which are not directly re ected by the behaviour of the pressure drop versus time curve. However, these phenomena are shown to a ect the distribution of collected soot mass in the di erent channels of the lter and, consequently, the regeneration behaviour. The evolution of ow maldistribution was also studied in a number of regeneration experiments. It was con rmed that the variation of the volatile organic fraction in the lter and the associated partial catalytic regenerations at low temperatures interact with ow and soot maldistribution in a complex way. The conclusions from this study set the scene for future, more detailed investigations that are expected to improve understanding and modelling of diesel lter pressure drop and regeneration characteristics. Keywords: diesel exhaust emissions, diesel particulate lters, catalytic soot incineration, volatile organic fraction, ow maldistribution m dynamic viscosity (Pa s) NOTATION r density (kg/m3) (rk) p soot layer density times permeability A area (m2) product (kg/m) E substrate thickness (m) k permeability (m2) m mass (kg)

This paper involves an experimental investigation of the role of the volatile organic fraction ( VOF ) adsorbed on the diesel particulate, in the initiation of regeneration of a SiC diesel lter installed on a modern diesel engine, run on catalytic additive-doped fuel. VOF adsorption-desorption and oxidation behaviour is mainly determined by performing a thermogravimetric analysis ( TGA) of samples collected directly from a SiC lter installed on the engine running under low-and mediumspeed and low-and medium-load conditions, as more representative of city driving. Based on the TGA analysis results, the percentage VOF content in soot was calculated and mapped as a function of engine speed and load in the range of investigation. The e ect of adsorbed hydrocarbons on the regeneration behaviour was assessed by comparing regeneration experiments with the stepwise load increase for a lter loaded with soot at di erent VOF concentration levels. The appearance of a number of incidents of stochastic regeneration behaviour during loading at low exhaust temperatures with a relative high VOF content was observed and discussed. An e ort was made to correlate regeneration rate with the VOF content in soot and the prevailing engine operation point during loading. This work aims at better understanding of diesel lter behaviour with modern diesel engines and also aims to support improved modelling of fuel-additive assisted regeneration by use of fuel additives at low temperatures (150-400°C ).