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Under high-pressure conditions such as those existing in a common-rail system, a serious concern is the possibility of wax precipitation from diesel fuels and the consequent deterioration in the diesel engine performance, even if the temperature is higher than the CP (cloud point) of the fuel. By using a diesel engine with a common-rail system, high-acceleration tests were performed under high-load conditions for three test fuels, which correspond to Japanese JIS grade 2 diesel fuels but have different cold-temperature properties, at a temperature exceeding their CPs. The test revealed differences in the engine speed and the throttle position among the test fuels. It was suggested that there was a possibility of a fault in fuel injection caused by the wax precipitation at high pressure.

The storage stability of diesel fuels containing 5% fatty acid methyl esters (FAMEs) was investigated at normal, high, and low temperatures. Unsaturated FAMEs such as rapeseed methyl ester (RME) or soy methyl ester (SME) oxidized to yield peroxides and acids during high-temperature (100 °C) storage. On the other hand, diesel fuels blended with a saturated FAME such as palm methyl ester (PME) showed stable oxidation performance during high-temperature storage. The cold flow properties of PME-blended diesel fuels, such as cold flow plugging point (CFPP) and pour point, deteriorated during the low-temperature storage; this led to deterioration of the drivability of vehicles using this type of diesel. Furthermore, in the PME-blended diesel fuels, crystals of saturated fatty acid glyceride were formed during normal-temperature storage (10 to 15 °C) above the cloud point (CP) of the fuels.

The effects of ethyl tertiary butyl ether (ETBE) and ethanol (EtOH) blending in gasoline on particulate matter (PM) emissions were investigated for a direct-injection spark ignition vehicle running on a chassis dynamometer. The test was performed under constant-speed conditions and 10.15-mode and 11-mode cycles. The total number of particles was measured by using a condensation particle counter (CPC). It was observed that the number of particles was affected by the amount of aromatics in the fuel and T90 (the distillation temperature where 90 vol.% of the fuel is evaporated), which was caused by the blending of the oxygenated compounds. The impact of T90 on the number of particles was greater for the 11-mode cycle than for the 10.15-mode one.

Newly designed laboratory measurement system, which reproduces particle number size distributions of both nuclei and accumulation mode particles in exhaust emissions, was developed. It enables continuous measurement of nano particle emissions in the size range between 5 and 1000 nm. Evaluations of particle number size distributions were conducted for diesel vehicles with a variety of emission aftertreatment devices and for gasoline vehicles with different combustion systems. For diesel vehicles, Diesel Oxidation Catalyst (DOC), urea-Selective Catalytic Reduction (urea-SCR) system and catalyzed Diesel Particulate Filter (DPF) were evaluated. For gasoline vehicles, Lean-burn Direct Injection Spark Ignition (DISI), Stoichiometric DISI and Multi Point Injection (MPI) were evaluated. Japanese latest transient test cycles were used for the evaluation: JE05 mode driving cycle for heavy duty vehicles and JC08 mode driving cycle for light duty vehicles.

Crosscheck tests of fast electrical mobility spectrometers, Differential Mobility Spectroscopy (DMS) and Engine Exhaust Particle Sizer(EEPS), were conducted to evaluate the accuracy of fine particle measurement. Two kinds of particles were used as test particles for the crosscheck test of instruments: particles emitted from diesel vehicles and diluted in a full dilution tunnel, and particles generated by CAST. In the steady state tests, it was confirmed that the average concentration of each instrument was within the range of ±2σ from the average concentration of all the same type of instruments. In the transient tests, it is verified that the instruments have almost equal sensitivity. For application of the fast electrical mobility spectrometers to evaluation of particle number and size distributions, it is essential to develop a calibration method using reference particle counters and sizers (CPC, SMPS, etc.) and maintenance methods appropriate for each model.

In order to clarify future automobile technologies and fuel qualities to improve air quality, second phase of Japan Clean Air Program (JCAPII) had been conducted from 2002 to 2007. Predicting improvement in air quality that might be attained by introducing new emission control technologies and determining fuel qualities required for the technologies is one of the main issues of this program. Unregulated material WG of JCAPII had studied unregulated emissions from gasoline and diesel engines. Eight gaseous hydrocarbons (HC), four Aldehydes and three polycyclic aromatic hydrocarbons (PAHs) were evaluated as unregulated emissions. Specifically, emissions of the following components were measured: 1,3-Butadiene, Benzene, Toluene, Xylene, Ethylbenzene, 1,3,5-Trimethyl-benzene, n-Hexane, Styrene as gaseous HCs, Formaldehyde, Acetaldehyde, Acrolein, Benzaldehyde as Aldehydes, and Benzo(a)pyrene, Benzo(b)fluoranthene, Benzo(k)fluoranthene as PAHs.