Search Results

The design of a diesel particulate trap system to fit a specific vehicular application requires significant expenditure, due to the high degree of interaction between the vehicle operation and trap behavior. The assistance of modeling in the design process is already well established. This paper presents the basic principles of a Computer Aided Engineering methodology aimed to assist the selection of the basic parameters of a Diesel Particulate Trap System by reducing the number of the necessary experimental tests. The computational modules currently supporting the CAE methodology are based on fundamental mathematical models, incorporating a small number of semi-empirical relations derived by experimental data on trap loading and catalytic regeneration, exhaust system heat transfer and trap backpressure effect on fuel consumption.

The purpose of this paper is to investigate a new, universally applicable technique to protect the filter from overheating that could overcome the need for trap bypassing; namely, the trap protection by limiting A/F ratio during regeneration. The technique is supported by control of A/F ratio, leading to an indirect control of exhaust oxygen content and consequently trap regeneration rate. Realisation of the above-mentioned, very simple idea, so as to work effectively in the multitude of possible trap failure scenarios occuring during vehicle driving, is shown to be a fairly complicated task. The new method of trap protection, now being at the stage of initial investigations, is expected to lead to a safe and reliable system with wide applicability, without the need to bypass the trap at any circumstances. As such, it will also be attractive for passenger car applications, supported by the recent advances in wide application of electronic fuel control.

In view of recent and future US and european regulations the design optimization of 3-way catalytic converters (3WCC) should also account for catalyst durability. The purpose of this paper is to extend the authors' approach for 3WCC modeling and evaluation in the direction of covering some aspects of ageing behavior. After a brief examination of the commonly accepted ageing mechanisms, a new methodology for the assessment of catalyst durability is formulated. This methodology takes into account the effect of thermal loading, high-temperature oxidation and poisoning of the catalyst. Based on the approach presented, along with the 3WCC and other related models and computer codes already in-use by the authors, a comparative assesment of engine bench ageing cycles may be computationally supported. Correlation of vehicle ageing cycles with engine bench cycles may also be accomplished as illustrated by a case study.

An automatic forced regeneration ceramic trap system with throttling before the trap, using Ce based fuel additives, for installation on light-duty diesel passenger cars is described. The system was installed on two vehicles and tested in the laboratory. The repeatability of the back pressure variation due to the soot accumulation during successive FTP cycles was determined, and the operation period of the system was defined. The operation of the system in both applications was equivalent to about 35 km of urban driving. The filtration efficiency approached 80% in FTP cycle and 90% in ECE and JAPAN 13 mode tests, while gaseous emissions and fuel consumption were practically not affected by the system.

The modeling of transient phenomena occurring inside an automotive 3-way catalytic converter poses a significant challenge to the emissions control engineer. Since the significant progress that has been observed with steady-state models cannot be directly exploited in this direction, it is necessary to develop a fully transient model and computer code incorporating dynamic behaviour of the three way catalytic converter in a relatively simple and effective way. The Laboratory of Applied Thermodynamics (LAT), Aristotle University Thessaloniki, is cooperating with the Engine Direction of FIAT Research Center, in the development of a computer code fulfilling these objectives, within the framework of an EEC Brite EuRam cost shared project. The CRF and LAT modeling approaches, along with the underlying philosophy and experimental work, are presented in this paper.

This paper presents the experience gained by testing a trap system on a turbocharged bus engine. The trap is placed before the turbo in order to fully exploit the high regeneration potential of the turbocharged engine. This of course necessitates a new consideration of the turbocharging system, in order to keep a good turbocharger response. The quick temperature response of the light-weight exhaust manifold installed with the system, partially offsets in this respect the thermal inertia of the ceramic trap. The effects of the use of Cerium or Copper-based fuel additives enhancing regeneration capability are presented, in order to allow preliminary assessment of optimization capabilities for the final version of the system to be used with the bus. Regeneration of this system is effected through the application of exhaust throttling before the trap. The bypass technique is also applied for trap protection.

This paper presents a computational model of the transient behaviour of trap systems. The model is applicable to various driving scenarios, vehicle, engine, and trap types, as well as different trap regeneration and protection techniques. The model is synthesized from existing submodels covering the vehicle kinematics, diesel engine operation, trap operational characteristics, and the trap regeneration and protection hardware performance. The model is applied to a parametric investigation of the transient operation of the Laboratory of Applied Thermodynamics (LAT) trap oxidiser system fitted on a Mercedes 200D passenger car. The major tasks of the investigation were (a) the evaluation of the control philosophies as regards their influence on vehicle driveability, fuel consumption, and by-pass operation time, (b) the evaluation of protection techniques such as lambda-control and trap by-passing with the trap subjected to a number of failure scenarios.

Exhaust temperature response is very important in the design of exhaust aftertreatment systems. Analysis of this response is made in this paper by means of heat transfer calculations at the exhaust system, leading to a model that predicts exhaust system and exhaust temperature response. Thus, the effect of differences in design of exhaust system components may be studied for optimization purposes. The model is readily extended to predict heating response of ceramic honeycomb filters. An approximate method for quick computation of exhaust system response based on the response of individual components, is also presented to facilitate the computations.

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.

In SAE paper No. 860293, the first conclusions from application of the technique of forced regeneration of the ceramic trap by exhaust throttling of the diesel engine had been presented. The presentation is integrated in this paper, by a thorough interpretation and modelling of the effect of exhaust throttling on the diesel engine operation characteristics and thermal loading, as well as a discussion of the possibility and particularities of application to different types of engines. Behavior of the exhaust throttled 4-stroke diesel engine is exhaustively analyzed by use of computer simulation. Computer models are also used to study the effect of exhaust throttling on the diesel engine thermal loading. The validity of the results is tested by a large number of measurements conducted in the LAT the last five years.

A ceramic trap forced regeneration system for urban buses and passenger cars, capable of safe and reliable on-road regeneration is presented in this paper. Development of this system has been made possible through the application of two main design aims: The possibility of protecting the trap from overheating by use of a trap bypassing technique, and the reduction of the total mass of intervening parts between engine and trap, so as to improve trap temperature transient response.

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.

A Diesel particulate trap oxidiser system suitable for retrofiting on urban buses is described. The system consists of a ceramic trap, a regeneration device and a control unit. The system is based on a new forced regeneration technique, by means of exhaust gas throttling. This technique establishes regeneration conditions on the road by the engine itself, with-out any external source of thermal energy or catalyst. Two buses in use with the Athens Public Transport Company (EAS) have been equipped with this system. The buses have been tested under real conditions on Athens urban bus routes and the results after the first 10000 km of operation are presented.

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 model simulating the behavior of the porous ceramic trap was developed. The model is based on the assumption that the pore size of the trap combined with the particle size distribution resulting from the trap oxidising activity defines two areas of trap operation: Ci) accumulation when no pass-through is permitted, and (ii) continuous regeneration when pass-through is permitted. The mathematical evaluation of the model demonstrates that regeneration depends on the ratio of space-time and oxidation process time constant. As far as the lower regeneration limit is concerned, temperature is the main parameter, while the upper regeneration limit is imposed by the low space-time. These dependencies have been experimentally confirmed for the couple of a light-duty Daimler-Benz engine and a Corning EX 47 trap. The test data at the regeneration limits have been correlated on the basis of the model and for continuous oxidation of particle mass flow.

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.