Kiyoshi Kobashi

Evaluation of Burned Gas Ratio (BGR) as a Predominant Factor to NOx

Experiments were conducted with four cylinder production engines to evaluate the effect of EGR and mixture stoichiometry on NOx by measuring the burned gas ratio in the cylinder (BGR) by using a gas sampling valve and CO//2 gas analyzer. The total gas fuel ratio (G/F) in the cylinder, which is a function of air-fuel ratio (A/F) and BGR and is some measure of adiabatic combustion peak temperature of charge, was introduced as a new measure to evaluate the combustion in the cylinder. G/F ratio coupled with A/F could be utilized to evaluate the combustion characteristics such as NOx emission, misfire limit, etc. in various combustion chamber configurations. NOx emission and misfire limit are strongly affected by the BGR in the cylinder. Stoichiometrically burned gas EGR has the best potential to reduce NOx together with power for a fixed engine displacement, but from the point of view of fuel economy and misfire limit indicated by G/F, its mixture is the second to leanest A/F, when the critical constraint of NOx and better fuel economy were considered.

Regenration Process of Ceramic Foam Diesel-Particulate Traps

Periodic regeneration of the diesel particulate trap is essential to maintain the collection efficiency and exhaust gas back 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. Additional energy is required above normal engine operating conditions to initiate the incineration under lower exhaust gas temperature. Regeneration must be carried out within a narrow range of particulate loading to avoid the melting of the filter material. The effects of fuel additives have been estimated by using the mathematical simulation.