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The Miller system was implemented to control the intake-air throttle valve for a stationary natural gas engine. The throttle system consists of an additional rotary valve provided with a variable timing device and a conventional butterfly valve. This throttle system can control not only the mass flow rate of the air-fuel mixture by changing the intake duration, but also the effective compression ratio at the same time. The experimental results showed an improvement in thermal efficiency at part load and a reduction of NOx emissions for the gas engine.

A program to demonstrate high thermal efficiency of a heat insulated turbocompound diesel engine was carried out. Major problems were choosing proper heat resisting materials, obtaining high mechanical and thermal efficiency of components, providing lubrication oil which works at high temperature and controling heat flux from a combustion chamber. A six cylinder, 125mn bore, turbocharged diesel engine was chosen for this program. Ceramic coating was mainly employed as a means of insulating heat and protecting engine parts. For the heat insulation, a ductile cast iron piston coated with ZrO2 was used and the cooling water was entirely eliminated. Heat flow analysis was conducted both analytically and experimentally. Thus, heat rejection was reduced by about 35%. While maximum temperature of the cylinder wall was raised up to 350°C, no scuffing and excessive wear took place in the sliding parts of a single cylinder engine for 500 hours.

A six cylinder direct-injection diesel engine of 105 mm bore was modified for heat insulation and turbo-compounding. The insulation was provided by entirely eliminating cooling water and replacing major hot parts with the ones having air gap or ceramic insulator in their structure. The engine was run with three different fuel; Diesel fuel with 52 and 30 cetane number and coal derived fuel, SRC-II. Due to the elevated temperature of combustion chamber in the insulated engine, ignition delay was significantly shortened and helped to burn the low cetane fuel. The engine could run with SRC-II, cetane number less than 10, though the rate of pressure rise was excessive at light load. Cylinder liner temperature was almost 400°C and way above the empirical limit for conventional water cooled engine but the engine could complete a couple of 250 hour durability test.