Search Results

Degradation of the deNOx performance has been found in in-use heavy-duty vehicles with a urea-SCR system in Japan. The causes of the degradation were studied, and two major reasons are suggested here: HC poisoning and deactivation of pre-oxidation catalysts. Hydrocarbons that accumulated on the catalysts inhibited the catalysis. Although they were easily removed by a simple heat treatment, the treatment could only partially recover the original catalytic performance for the deNOx reaction. The unrecovered catalytic activity was found to result from the decrease in conversion of NO to NO2 on the pre-oxidation catalyst. The pre-oxidation catalyst was thus studied in detail by various techniques to reveal the causes of the degradation: Exhaust emission tests for in-use vehicles, effect of heat treatment on the urea-SCR systems, structural changes and chemical changes in active components during the deactivation were systematically investigated.

The emission reduction from diesel engines is one of major issues in heavy duty diesel engines. Super Clean Diesel (SCD) Engine for heavy-duty trucks has also been researched and developed since 2002. The main specifications of the SCD Engine are six cylinders in-line and 10.5 l with a turbo-intercooled and cooled EGR system. The common rail system, of which the maximum injection pressure is 200 MPa, is adopted. The turbocharger is capable of increasing boost pressure up to 501.3 kPa. The EGR system consists of both a high-pressure loop (HP) EGR system and a low-pressure loop (LP) EGR system. The combination of these EGR systems reduces NOx and PM emissions effectively in both steady-state and transient conditions. The emissions of the SCD Engine reach NOx=0.2 g/kWh and PM=0.01 g/kWh with aftertreatment system. The adopted aftertreatment system includes a Lean NOx Trap (LNT) and Diesel Particulate Filter (DPF).

Urea SCR (Selective Catalytic Reduction) system has high potential of reducing NOx. But such as system durability and safety under deteriorated catalysts conditions have not been well enough clarified because it is new technology for vehicles. In this paper, current NOx emission level of an engine equipped with urea SCR system is discussed and then exhaust emission characteristics were analyzed when the SCR catalyst and/or oxidation catalyst lose their functions. When both SCR and oxidation catalyst were de-activated, not only NOx but also PM increased remarkably, which were much more than the engine-out emissions. Oxidation catalyst downstream of SCR catalyst was effective to suppress such deteriorations.

Particulate Matter (PM) from diesel engines is thought to be seriously hazardous for human health. Generally, it is said that the hazard depends on the total number and surface area of particles rather than total mass of PM. In the conventional gravimetric method, only the total mass of PM is measured. Therefore, it is very important to measure not only the mass of PM but also size and number density of particulates. Laser-Induced Incandescence (LII) is a useful diagnostic for transient measurement of soot particulate volume fraction and primary particle size. On the other hand, Scanning Mobility Particle Sizer (SMPS) is also used to measure the size distribution of soot aggregate particulates at a steady state condition. However, the measurement processes and the phenomena used to acquire the information on soot particulate are quite different between the LII and SMPS methods. Therefore, it is necessary to understand the detailed characteristics of both LII and SMPS.

Flash-boiling occurs when a fuel is injected to a combustion chamber where the ambient pressure is lower than the saturation pressure of the fuel. It has been known that flashing is a favorable mechanism for atomizing liquid fuels. On the other hand, alternative fuels, such as gaseous fuels and oxygenated fuels, are used to achieve low exhaust emissions in recent years. In general, most of these alternative fuels have high volatility and flash-boiling takes place easily in fuel spray, when they are injected into the combustion chamber of an internal combustion engine under high pressure. In addition, fuel design concept the multicomponent fuel with high and low volatility fuels has been proposed in the previous study in order to control the spray and combustion processes in internal combustion engine. It is found that the multicomponent fuel produce flash-boiling with an increase in the initial fuel temperature.

Fuel design for internal combustion engines has been proposed in our study. In this concept, the multicomponent fuel with high and low volatility fuels are used in order to control the spray and combustion processes in internal combustion engine. Therefore, it is necessary to understand the spray and combustion characteristics of the multicomponent fuels in detail. In the present study, the modeling of multicomponent spray vaporization was conducted using KIVA3V code. The physical fuel properties of multicomponent fuel were estimated using the source code of NIST Mixture Property Database. Peng-Robinson equation of state and fugacity calculation were applied to the estimation of liquid-vapor equilibrium in order to take account for non-ideal vaporization process. Two-zone model in which fuel droplet was divided into droplet surface and inner core was introduced in order to simply consider the temperature distribution in fuel droplet.

Nitrous oxide (N2O) is a strong green house effect gas and three-way catalyst is one of the major sources. N2O is mostly emitted at temperatures during the process of light off in the catalyst and the frequency of this temperature range over total temperature range distribution affects strongly on N2O emission. The effect of cold ambient on N2O emission was analyzed based on N2O-catalyst temperature characteristics and catalyst temperature data gained by road driving test at north part of Japan in winter. As results, N2O emission may drastically increase in colder cities and winter city traffic conditions.

Fuel composition is investigated as a parameter influencing fuel/air mixing of direct injected fuel and the subsequent consequences for particulate emissions. Presumably, enhanced mixing prior to ignition results in a larger portion of fuel burning as a premixture and a smaller portion of diffusion burning around fuel-rich regions. This would potentially lower particulate emissions without overly compromising hydrocarbon emissions or high load operation. Using mixtures of n-paraffin fuels, particulate emissions were measured and the results were compared with in-cylinder visualization of the injection process and two-color method calculations of flame temperature. In general, lower boiling point fuels exhibited higher flame temperatures, less visible flame, and lower particulate emissions.