Search Results

A regeneration of a wall-flow monolith filter with a heater unit was examined. In the preliminary test the regeneration showed unsatisfactory results, back pressure level increased and filter melting occured. Reversing the gas flow through the filter during the regeneration process and initiating particulate combustion from the outlet side of the filter was found to be a solution for the filter melting problem in particular. This “reverse regeneration” system, which we call RRG, compared with a conventional regeneration (CRG) was examined with a model reactor and applied on an actual vehicle on a chassis dynamometer. Tests confirmed that filter melting was prevented, however cracking of the filter could not be prevented with an RRG.

To reduce diesel odor its first essential that a simple but accurate method of measuring odor level be available. Various approaches were considered but found to give poor correlation to the odor intensity as assessed by professional perfumers. However a method utilizing a cold trap and measurement of the odor components' pH correlated very closely to the human olfactory sense. This method proved capable of accurately measuring even small changes in odor level and was applied to a study of the effects on odor Levels of changes in engine specifications and operating conditions. The results indicated that squish area geometry greatly affects diesel odor.

Regeneration experiments were carried out for the establishment of a particulate combustion model. Distributions of the filter temperature and gas temperature, the concentration of the oxygen in the filter, and combustion products were simultaneously measurd. Numerical simulations were performed by two steps. As the first step, a quasi one-dimensional simulation model was applied to the estimation of propagation characteristics of the particulate combustion, such as flame velocities, and the filter temperature change with time. Air velocity and heat capacity of the filter were found to be important factors for the combustion propagation. As the second step, a two-dimensional axisymmetric simulation program for the regenerative combustion was developed and coupled with a FEM stress analysis program “MARC”.

Regeneration capability of a wall-flow monolith type diesel paticulates filter with an electric heater was studied. To prevent filter crack generation and unburned particulates accumulation, a precision controller was added to the test equipment to reduce thermal load. In order to control the supply of oxygen to potentially prevent cracking, a second air feeder was also added. Furthermore, to ignite the accumulated particulates uniformly and propagate extensively to burn accumulated particulates completely a newly improved heater unit was employed. Repeated regeneration tests were conducted with cars on a chassis dynamometer. Though crack generation and unburned particulates accumulation were reduced considerably, satisfactory prevention could not be achieved. Therefore a parameter study using regenerative burning and thermal stress analysis model was carried out.

Periodic regeneration of the diesel particulate trap is essential to maintain the collection efficiency and exhaust gas hack pressure at acceptable levels. The objectives of this study are to describe the phenomenology of ceramic foam filter regeneration process and to present its mathematical model. Further simulation study is carried out to estimate the effects of various factors including fuel additive on the ignition and the filter bed temperature and to investigate conditions of excessive temperature which could result in filter destruction. The model is based on the assumption that the regeneration process is composed of two steps. The first step is the additional heat supply from the external energy source, and the second step is the spontaneous combustion propagation. The results from the analytical model agreed very well with the experimental results.

To elucidate the effects of EGR, the gas compositions in the cylinder at the end of the compression stroke, have been analyzed. The relationship of the burned gas fraction in the cylinder (defined as BGR) to NOx emission and misfire limit have been investigated and imply the following: 1) NOx and misfire limit are strongly affected by the BGR at specified air fuel ratio and spark timing. 2) Gas-fuel ratio which is the ratio of the total gas to the fuel in the cylinder is the predominant factor used extensively to evaluate the effects of EGR and/or lean mixture on NOx and misfire limit of an engine.

The white smoke generated by a diesel engine was analyzed and found to consist mainly of hydrocarbons. Test results indicated that the emission level depends on ambient temperature. A compact white smoke meter was developed to enable emission levels to be accurately measured. The internal temperature of this meter is controlled so that white smoke is generated within the measuring device. The meter was used to evaluate the effectiveness of various white smoke emission control devices for the DI diesel engine. The results indicated that an intake air heater offers the greatest potential. Accordingly, a new intake air heater with ceramic PTC thermistor having a very high heating efficiency was developed to reduce white smoke emission.