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In Biodiesel Fuel Research Working Group(WG) of Japan Auto-Oil Program(JATOP), some impacts of high biodiesel blends have been investigated from the viewpoints of fuel properties, stability, emissions, exhaust aftertreatment systems, cold driveability, mixing in engine oils, durability/reliability and so on. In the impact on exhaust emissions, the impact of high biodiesel blends into diesel fuel on diesel emissions was evaluated. The wide variety of biodiesel blendstock, which included not only some kinds of fatty acid methyl esters(FAME) but also hydrofined biodiesel(HBD) and Fischer-Tropsch diesel fuel(FTD), were selected to evaluate. The main blend level evaluated was 5, 10 and 20% and the higher blend level over 20% was also evaluated in some tests. The main advanced technologies for exhaust aftertreatment systems were diesel particulate filter(DPF), Urea selective catalytic reduction (Urea-SCR) and the combination of DPF and NOx storage reduction catalyst(NSR).

Nissan Diesel Motor Co.,LTD have developed a new turbocharged diesel engine with a variable nozzle turbocharger for the purpose of solving the contradictory problems of mobility and fuel economy, while meeting the 1990 Japanese emission standards. The heavy-duty trucks equipped with this new turbocharged engine have been released in the market recently. The variable nozzle turbocharger capable of maintaining sufficient turbine efficiency over the broad range of engine operating band was jointly developed with Allied Signal, Garrett Automotive Group in United States of America.It's control method, a stepless boost pressure feedback control system, was newly developed in order to make the most effective use of the turbocharger.

The characteristics of a new diesel particulate filter material made of SiC were studied through engine tests in varying material properties, such as average pore diameter, and wall thickness. Compared to a conventional cordierite filter of the same size, particulate trapping efficiency is almost the same, and the pressure loss and the deterioration of fuel consumption can be reduced to about half with the optimum material properties. If the same pressure loss is allowed, the filter size can be reduced by 30%. Its good thermal conductivity prevents local temperature increases, which doubles the permissible amount of trapped particulates. As heat crack problems occurred in integral-type filters due to the high thermal expansion of SiC, a split-type filter having 49 filter segments with a square section was developed.

Injection process simulation methods were developed for both the unit injector (UI) system and the pump-line nozzle (PLN) system consisting of an in-line injection pump, fuel line, and nozzle. Simulation results agreed well with measured ones. With regard to the shape of injection rate and the peak injection pressure change at various engine speeds, the injection characteristics of the UI system are better than those of the PLN system. Simulation results showed that similar injection characteristics can also be obtained with the PLN system by using a concave cam with a carefully designed cam profile for a sleeve-controlled in-line injection pump and by changing the prestroke according to the operating conditions. Engine test results demonstrated the possibility of improving the trade-off between NOx and fuel consumption by shaping the injection rate. The shape of injection rate plays an important role in diesel combustion(1,2)*, affecting exhaust emissions and also combustion noise.

Engine manufactures are continuing to develop new engine designs that provide higher power output, lower fuel consumption and lower engine weight. In order to achieve significant engine weight reduction, the light weight cylinder block structure employs dry cylinder liners rather than wet cylinder liners. The cast iron dry liner structure is utilized because of the superior wear and scuff resistance of the cast iron. Thin wall dry cast iron liners are being employed in both gasoline and diesel engines. Dry cylinder liners with wall thickness of 1.5mm are in production for Japanese automotive diesel engines. In the case of the dry thin wall cast iron liners, two(2) design configurations are employed: Loose-fit type having a specified clearance between the outer liner surface and the cylinder bore surface. Press-in type having an interference fit between the outer surface of liner and the cylinder bore surface.

In Japan there is currently a strong social demand for exhaust emissions reduction from heavy-duty diesel engines. Therefore, new Long-Term Regulation will come into effect in October 2005, setting the NOx standard at 2.0 g/kWh and the PM standard at 0.027 g/kWh. At the same time, customers always demand exceptional fuel economy from heavy-duty commercial vehicles. A urea-based Selective Catalytic Reduction (SCR) system was developed to satisfy both these demands, and will be introduced in the fall of 2004. The operating conditions of vehicles in Japan are different from those in the US and Europe. Basically, average vehicle speeds are significantly lower. To improve the low temperature SCR performance, an oxidation catalyst was located upstream of the SCR, and an additional oxidation catalyst was located downstream of the SCR for emergency NH3 slip. The muffler size with all three catalysts was similar to a conventional muffler.

Evaporative cooling was applied to a heavy duty diesel engine to investigate the feasibility of this cooling method. Engine test results showed the following benefits of this cooling method: Reduction of the size of theradiator and cooling fan is feasible. The maximum temperature of the combustion chamber wall did not increase, though the coolant temperature rose by 20°C. The fuel consumption could be reduced especially at partial load. Engine warm-up performance was significantly improved. An oil cooler rig test was also conducted to investigate the heat transfer characteristics of the oil cooler with evaporative cooling.