Yukihiro Tsukasaki

Effects of Cetane Number and Distillation Characteristics of Paraffinic Diesel Fuels on PM Emission from a DI Diesel Engine

Fischer-Tropsch Diesel (FTD) fuel is expected to be a promising clean diesel fuel in the future because of its characteristics of zero sulfur, zero aromatics and a high cetane number. However, the optimum fuel properties for diesel engines have not been realized. In this study, the effects of cetane number and distillation characteristics on engine-out PM emissions from a conventional direct injection diesel engine were investigated by using paraffinic fuels which were made to simulate FTD fuel. From the results of the vehicle exhaust emissions test and engine dynamometer test, it was found that the narrow distillation characteristics (which eliminates heavy hydrocarbon fraction) could reduce the soluble organic fraction (SOF) in PM emissions, and the excess high cetane number characteristic promoted the formation of insoluble organic fraction (ISOF). It is considered that shorter ignition delay due to the excessively high cetane number results in poor mixing of injected fuel and air in the combustion chamber. Future diesel engines are expected to lower the compression ratio and to require the fuels with high cetane number. However, in the case of conventional diesel, the results showed that moderate high cetane number and narrow distillation properties eliminating the heavy hydrocarbon fraction were desirable as the optimum FTD fuel.

Effect of Sulfur-free and Aromatics-free Diesel Fuel on Vehicle Exhaust Emissions using Simultaneous PM and NOx Reduction System

A new diesel after-treatment system, Diesel Particulate and NOx Reduction System (DPNR), is being developed for reducing PM and NOx emissions. We examined the effects of sulfur content in lubricants on exhaust NOx emission from DPNR catalyst, and examined the PM reduction ability using sulfur-free and aromatics-free fuel. After vehicle durability testing of 40,000 km without forced regeneration of PM and sulfur poisoning on DPNR catalyst, deterioration of DPNR was lower than using higher sulfur contents in fuel and oil. In addition to decreasing fuel sulfur, decreasing oil sulfur was also effective to maintain high NOx conversion efficiency. Although the catalyst was poisoned by sulfur in the lubricants, the influence of oil sulfur poisoning on the catalyst was lower than fuel sulfur poisoning. On the other hand, engine out PM emissions decreased by 70 % because of aromatics-free fuel. The pressure drop of DPNR did not increase during the 40,000 km vehicle durability test. Engine-out PM emissions are much lower than the PM oxidation capability of the catalyst. Thus, the combination of sulfur-free and aromatics-free fuel with the DPNR system effectively maintains low PM and NOx emissions, and reduces the frequency of regeneration due to PM accumulation and sulfur poisoning.

Effect of Hydrocarbon Molecular Structure on Diesel Exhaust Emissions Part 2: Effect of Branched and Ring Structures of Paraffins on Benzene and Soot Formation

In order to determine diesel fuel characteristics that might influence particulate matter (PM) emission, we have conducted a detailed investigation that combines combustion/exhaust emission measurements, in-cylinder observations, fuel analyses and chemical reactor experiments. A comparison between three representative diesel fuels, viz., “Base” (Japanese market fuel), “Improved”(lighter fuel with lower aromatics) and Swedish “Class-1” yielded the following results: (1) The amount of PM emission decreases in the order of “Base” > “Class-1” > “Improved”. Unexpectedly enough, “Class-1” produces more PM than “Improved” despite its significantly lower distillation temperature, and lower aromatics and sulfur content. (2) There is little difference in the combustion characteristics of the three fuels. (3) Only “Class-1” contains significant quantities of iso and naphthenic structures. (4) Flow reactor pyrolysis shows that “Class-1” produces the largest amount of PM precursors, such as benzene and toluene. These results suggest that the presence of branched and ring structures can increase exhaust PM emissions. This finding was confirmed by flowreactor and shock tube experiments using hexanes, which revealed that isoand cycloparaffins produce more benzene and soot than n-paraffins do. The results obtained in this study indicate that the specific molecular structure of the paraffinic components needs to be considered as one of the diesel fuel properties closely related to PM formation.

Development of the second generation methanol lean burn system

The second generation methanol lean burn system has been developed. Lean misfire limit was extended by using a swirl control valve in the intake port which improves combustion under partial load. An EGR system has been newly adopted to reduce NOx emissions and a under-floor type catalyst is also used to reduce formaldehyde emission in the cold transient mode in addition to the manifold type catalyst