Search Results

N₂O is known to have a significantly high global warming potential. We measured N₂O emissions in engine-bench tests by changing the NO/NH₃ ratio and exhaust gas temperature at the oxidation catalyst inlet in a heavy-duty diesel engine equipped with a urea SCR (selective catalytic reduction) system. The results showed that the peak N₂O production ratio occurred at an exhaust gas temperature of around 200°C and the maximum value was 84%. Moreover, the N₂O production ratio increased with increasing NO/NH₃. Thus, we concluded that N₂O is produced via the NO branching reaction. Based on our results, two methods were proposed to decrease N₂O formation. At low temperatures ~200°C, NO should be reduced by controlling diesel combustion to lower the contribution of NO to N₂O production. This is essential because the SCR system cannot reduce NOx at low temperatures.

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.

To find a clue to reduction techniques for Nitrous Oxide (N2O) emission from three-way catalyst equipped vehicles, four test samples of three-way catalysts with typical noble metal compositions were fabricated by way of experiment and their N2O formation characteristics have been experimentally studied. Then, these catalyst samples were conditioned artificially by aging with real automotive exhaust gas and the N2O formation characteristics after aging has been also observed. As results, catalyst temperature zones and concentration levels of N2O formation varies greatly by the catalyst composition. In general, a catalyst with lower metal content showed lower N2O mass emission at both fresh and after aging conditions. The tendency of the increase in N2O mass emission due to the deterioration is also different among the tested catalyst samples.

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.

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.

A urea SCR system was combined with a DPF system to reduce NOx and PM in a four liters turbocharged with intercooler diesel engine. Significant reduction in NOx was observed at low exhaust gas temperatures by increasing NH3 adsorption quantity in the SCR catalyst. Control logic of the NH3 adsorption quantity for transient operation was developed based on the NH3 adsorption characteristics on the SCR catalyst. It has been shown that NOx can be reduced by 75% at the average SCR inlet gas temperature of 158 deg.C by adopting the NH3 adsorption quantity control in the JE05 Mode.

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.

To derive an effective technique for reducing a greenhouse gas nitrous oxide (N2O) emitted from automobiles, we prepared experimental three-way catalysts carrying various types and quantities of precious metals, and investigated their N2O generation and conversion characteristics. In view of previous reports on increased N2O emissions from in-use automobiles, we deactivated the catalysts in a rapid aging test, and observed the effect of catalyst deactivation on N2O generation and conversion by the catalysts. We found that the concentrations of generated N2O decreased as the quantities of precious metals carried by catalysts were decreased and that, accordingly, these low-carrying catalysts are more advantageous from the standpoint of reducing N2O generation. However, the concentrations of generated N2O increased as the catalysts were deactivated.

The engine in the research is a single cylinder DI diesel using the emission reduction techniques such as high boost, high injection pressure and broad range and high quantity of exhaust gas recirculation (EGR). The study especially focuses on the reduction of particulate matter (PM) under the engine operating conditions. In the experiment the authors measured engine performance, exhaust gases and mass of PM by low sulfur fuel such as 3 ppm and low sulfur lubricant oil such as 0.26%. Then the PM components were divided into soluble organic fraction (SOF) and insoluble organic fraction (ISOF) and they were measured at each engine condition. The mass of SOF was measured from the fuel fraction and lubricant oil fraction by gas chromatography. Also each mass of soot fraction and sulfate fraction was measured as components of ISOF. The experiment was conducted at BMEP = 2.0 MPa as full load condition of the engine and changing EGR rate from 0% to 40 %.