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This study investigates simultaneous improvement in thermal efficiency and cooling loss in the wider operating condition. To suppress the heat flux of the piston, the piston top and cavity were treated with thin thermal spraying of stainless steel. Thermal diffusivity of stainless steel (X5CrNiMo17-12-2, SUS316) is very low in comparison with the forged steel piston raw material (34CrMoS4, SCM435) to sustain local surface temperature at where spray flame directly interfered. In addition, its surface roughness was very fine finished aiming to reduce the convective heat transfer. The experimental results with the stainless-steel coated piston by utilizing a single cylinder engine showed the significant improvement in both cooling loss and thermal efficiency even in higher load operating conditions with compression ratio of 23.5:1.

For reducing exhaust emissions of heavy-duty diesel engines, the authors made an experimental study of diesel combustion using a single cylinder engine. The engine performance and exhaust emissions have been measured using a wide range and high EGR rate under the conditions of high boost intake pressure. The engine test cell has been equipped the external supercharger that is able to raise the boost pressure to 500 kPa, and also equipped the EGR system to increase the EGR rate until 50% under the 500 kPa boost condition. In various test conditions of load and engine speeds the authors have obtained the results, that is, NOx has been reduced drastically without increasing Particulate Matter (PM).

The biomass fuel is expected to solve the global warming due to a carbon neutral. A rapeseed oil methyl ester (RME) as biomass fuel was selected, and also a low sulfur diesel fuel is tested as reference fuel in this study. The experiments were carried out to improve diesel emissions and engine performance using high boost and high rate EGR system and a common rail injection system in a single cylinder engine. The diesel emissions and engine performance have been measured under the experimental conditions such as charging boost pressure from atmospheric pressure to 401.3kPa maximum and changing EGR rate from 0% to 40% maximum. RME contain about 10 mass % oxygen in the fuel molecule. Furthermore, RME does not contain aromatic hydrocarbons in the fuel. Due to these chemical properties, RME can be used at 40% high EGR condition.

For reducing NOx emissions, EGR is effective, but an excessive EGR rate causes the deterioration of smoke emission. Here, we have defined the EGR rate before the smoke emission deterioration while the EGR rate is increasing as the limiting EGR rate. In this study, the high rate of EGR is demonstrated to reduce BSNOx. The adapted methods are a high fuel injection pressure such as 200 MPa, a high boost pressure as 451.3 kPa at 2 MPa BMEP, and the air intake port that maintains a high air flow rate so as to achieve low exhaust emissions. Furthermore, for withstanding 2 MPa BMEP of engine load and high boosting, a ductile cast iron (FCD) piston was used. As the final effect, the installations of the new air intake port increased the limiting EGR rate by 5%, and fuel injection pressure of 200 MPa raised the limiting EGR rate by an additional 5%. By the demonstration of increasing boost pressure to 450 kPa from 400 kPa, the limiting EGR rate was achieved to 50%.

As a technology required for future commercial heavy-duty diesel engines, this study reexamines the potential of the multiple injection strategy for improving the thermal efficiency while maintaining low engine-out exhaust emissions with a high EGR rate of more than 50% and high boost pressure of 276.3 kPa abs under medium load conditions. The experiments were conducted with a single cylinder research engine. The engine was operated at BMEP of 0.8 MPa at a medium speed. Using multiple injections, the temporal and spatial in-cylinder temperature distribution was changed to investigate the effect on fuel consumption and exhaust emissions. The results showed that the multiple injection strategy combined with higher EGR rate could improve fuel consumption by about 3% due to the reduction of heat loss from the wall.