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In order to discuss future technical issues for urea SCR (selective catalytic reduction) system, it is necessary to assess various technical possibilities that would be applied to urea SCR systems which is capable of complying with future emission level requirements, for example Japanese 2009 emission regulation. In this paper, three measures (enhanced insulation on a DOC (diesel oxidation catalyst), aggressive urea solution injection and idling stop) are installed on a urea SCR system of a commercial engine system in order to achieve further NOx (nitrogen oxide) reductions. With combination of these three measures, NOx is drastically reduced to the levels lower than 0.7 g/kWh, which is a NOx limit value of the Japanese 2009 emission regulation. NH3 (ammonia) and HCN (hydro cyanide) are also measured as unregulated harmful components.

Homogeneous Charge Compression Ignition (HCCI) is effective for the simultaneous reduction of soot and NOx emissions from diesel engine. In general, high octane number and volatility fuels (gasoline components or gaseous fuels) are used for HCCI operation, because very lean mixture must be formed during ignition delay of the fuel. However, it is necessary to improve fuel injection systems, when these fuels are used in diesel engine. The purpose of the present study is the achievement of HCCI combustion in DI diesel engine without the large-scale improvements of engine components. Various high octane number fuels are mixed with diesel fuel as a base fuel, and the mixed fuels are directly applied to DI diesel engine. At first, the cylinder pressure and heat release rate of each mixed fuel are analyzed. The ignition delay of HCCI operation decreases with an increase in the operation load, although that of conventional diesel operation does not almost varied.

Particulate matter (PM) and polynuclear aromatic hydrocarbons (PAH) were measured under steady state engine operating conditions in the exhaust of a DI diesel engine that meets the Japanese 1994 heavy-duty vehicle standards. In this study, to examine and discuss the effects of pyrene and sulfur contents in fuels on PM and PAH emissions, experiments were performed using both ordinary diesel fuel and a specified fuel having simple hydrocarbon components and very few aromatics. In the experiments, pyrene and sulfur contents in the fuels were changed by the addition of reagents to the fuel. The following conclusions were obtained. (1) From the experiments using ordinary JIS No. 2 diesel fuel with a pyrene reagent added to yield 400ppm pyrene, it was found that pyrene addition brings about an increase in soluble organic fraction (SOF) under low load engine operating conditions.

The experiments were performed with two types of test engines, '72 model year type and '94 model year type engine, using both of conventional diesel fuel and synthetic diesel fuel, which has simple hydrocarbon components and no aromatics or sulfur content. SOF is extracted from the particulate sample exhausted out from the engines, then GC and GC-MS analyses were carried out. By comparing the results obtained, the role of high boiling point components in diesel fuel on SOF emission were observed. Further, by adding an artificially sulfur-containing compound and pyrene, which is a four ring polynuclear-aromatic-hydrocarbon (PAH), into the synthetic fuel, the effect of PAH content in fuel on PAH emission in SOF and the increase of SOF with increased sulfur content in fuel, were observed.

Engine experiments were carried out in order to investigate the mechanisms involved in connection with the emission of lubricant related polyaromatic hydrocarbons (PAH) from a D.I. diesel engine. In the experiments only the mechanisms related to pyrene emissions were investigated, since synthetic fuels and lubricants containing pyrene as the only aromatic compond were used. Particulate matter (PM) and the soluble organic fraction (SOF) of PM as well as PAH emissions were measured for different engine conditions at different levels of pyrene in the lubricant and the fuel. Possible mechanisms of PAH transportation from the lubricant to the exhaust gas are discussed based on the experimental results, as well as the importance of fuel and lubricant to SOF and PAH emissions.

The Thermogravimetry SOF measurement method is developed as simple and time-saving method. It is experimentally revealed that this method is useful for SOF measurement and the method has potential to distinguish SOF component. The oxidation catalysts can effectively reduce particulate matter under actual driving conditions. Sulfate formation suppressing oxidation catalyst reduces high molecular number paraffins. However, it is important for further development of oxidation catalyst to improve the oxidation ability of polar hydrocarbons included in SOF. The oxidation catalysts can effectively reduce CO, HC emissions under actual driving conditions. This is caused by the temperature rise of oxidation catalysts during accelerations.