Hisakazu Suzuki

Influence of catalyst deactivation on N2O emissions from automobiles

Abstract Though estimates of the total N 2 O emitted by automobiles differ widely, automobiles are believed to be a significant source of non-agricultural anthropogenic N 2 O emissions. At the Third Conference of the Parties (COP-3) UN Framework Convention on Climate Change, held in Kyoto in 1997, N 2 O was designated as a greenhouse gas whose release into the atmosphere must be reduced. This action increased the need for more accurate estimates of automotive N 2 O emissions. The wide variation in estimates may be attributed to differences in emission test modes, types of catalysts, and levels of catalyst deactivation involved in the tests. In this study, we examined the influence of automotive catalyst deactivation on N 2 O emissions from the perspective of catalyst temperature frequency distribution. Using a model gas and deactivated three-way catalysts (TWCs), we applied the exhaust emission test modes of various countries. The results indicate that the factor behind the increase of N 2 O emissions following catalyst deactivation is not growth in N 2 O generation, but a decline in the N 2 O decomposition capability of the catalyst. It was also found that the effect of catalyst deactivation differs according to the catalyst composition and the emission test mode.

Development of a Real-time NH3 Gas Analyzer Utilizing Chemi-luminescence Detection for Vehicle Emission Measurement

Recently, after-treatment techniques for diesel engine emission have made remarkable progress with the development of suitable De-NOx catalysts. The urea-injection SCR system is one of the candidates for a high efficiency De-NOx method for diesel engine emissions. This system reduces NOx through a reaction with ammonia (NH3) that is generated from injected urea. In this system, it is very important to control the amount and timing of the urea injection so as to minimize the NH3 gas slip. Therefore, NH3 gas measurement is becoming important during the development of NOx after-treatment systems even though NH3 is not a target component of the current emission regulations. In this paper, a new NH3 gas analyzer utilizing a chemi-luminescence detection (CLD) method has been developed. The new NH3 analyzer consists of dual detectors (DCLDs) and a furnace for a NH3 oxidization catalyst. Real-time concentration of NH3 can be calculated from the difference of NOx readings of two detectors. Basic performances such as response time and interference effect have been discussed here. Additionally, NH3 measurement in exhaust gas from a diesel engine vehicle with a urea-SCR system, as well as a lean burn gasoline engine vehicle with a three-way catalyst will be presented. Comparisons with conventional methods for NH3 measurement, such as fourier transform infra-red (FTIR) gas analyzer and soft ionization mass spectrometer (SIMS), are also described.

Effect of Boiling Point Differences of Two-Component Normal Paraffin Fuels on Combustion and Emission in CI Engines

The effect of boiling point difference as well as the flash boiling of two-component normal paraffin fuels on combustion and exhaust emission has been examined under different test conditions. To obtain a wide variation in boiling point between components different high boiling point fuels (n-undecane, n-tridecane and n-hexadecane) were blended with a low boiling point fuel (n-pentane) and different low boiling point fuels (n-pentane, n-hexane, and n-heptane) were blended with a high boiling point fuel (n-hexadecane). In addition the volume fraction of n-pentane was varied to have the best mixture ratio with n-tridecane. These fuel combinations exhibit different potential for flash boiling based on a certain ambient condition. The results indicate that though the potential for flash boiling is the highest for a mixture of n-pentane and n-hexadecane it emits about 20% higher PM than a mixture of n-pentane and n-tridecane. A mixture ratio of about 3:1 by volume of n-pentane and n-tridecane showed an advantageous level of flash boiling and yield the lowest emission at all injection timings and load ranges and is therefore proposed as a low emission fuel.

A Study on the Improvement of NOx Reduction Efficiency for a Urea SCR System

The urea SCR system is a major diesel NOx aftertreatment system. An ammonia slip catalyst (ASC) is located downstream of the SCR system to remove ammonia slipping from it, resulting in forming N2O having a significantly high global warming potential. Thus, we adopted dual-layered ASCs to identify how N2O is formed in the oxidation layer and how Zeolite layer thickness effects NH3 to N2O conversion characteristics. Engine tests and numerical simulations were conducted. The results show that Zeolite has a supplemental effect of reducing NOx and that an reduction in N2O formation is possible by increasing zeolite layer thickness while NH3 conversion is decreased. Thus, it is confirmed that zeolite layer thickness should be optimized to reduce these two emissions.

Modeling of Evaporation Process of Multicomponent Fuel Spray

Original KIVA code cannot take account for the spray and combustion processes of multicomponent fuels. Therefore, it is necessary to produce the sub-models for multicomponent fuel using KIVA code. In this study, the modeling of detailed physical properties and evaporation process for multicomponent fuel was conducted. In addition, the effects of fuel composition in multicomponent fuel on vapor distribution, spray tip penetration, vapor mass and evaporation rate, and sauter mean diameter were numerically investigated by using KIVA 3 V code with this multicomponent fuel spray model. From the numerical results, the spray characteristics of multicomponent fuel varied with a change in mixing fraction in multicomponent fuel. Especially, the evaporation of multicomponent fuel was not necessarily improved, even if much amount of high volatility fuel was mixed in the multicomponent fuel.