Shuichi Kajitani

A study of low-comression-ratio dimethyl ether diesel engines

Abstract A new concept of using dimethyl ether (DME) as an alternative fuel in direct injection compression ignition engines with low compression ratios was presented to seek a combustion regime with the highest thermal efficiency. The concept was experimentally evaluated by a comparison of performance and emissions between a DME-fuelled engine and the corresponding conventional diesel engine. The result demonstrated that the DME-fuelled engine is superior to the conventional diesel engine in terms of thermal efficiency, emissions and engine noise, particularly at low compression ratios. However, NOx emission is unacceptably high and needs to be reduced by exhaust gas recirculation (EGR) or after-treatment systems.

A Study of Dimethyl Ether(DME) Flow in Diesel Nozzle

Dimethyl ether (DME) holds promise as an alternative to diesel fuel. However, its physical properties are not similar to those of conventional diesel fuel. The P-V, bulk modulus and viscosity of DME are derived as a function of temperature and pressure. As a result, the Weber and Reynolds number of DME is very large as compared with that of diesel fuel. So, the spray characteristics of DME are not those of a liquid spray but similar to those of gas spray. The spray formation is strongly affected by the fuel flow in the nozzle. The Computational Fluid Dynamics (CFD) and experiments are examined to analyze the fuel flow in the nozzle. The DME physical properties make some difference to the flow in the nozzle, in comparison with those of diesel. As a CFD result, cavitation in the injection nozzle is more frequent with DME than with diesel oil. From experimental results, the temperature in the nozzle sac is higher with DME than with diesel oil. The state of DME in the sac changes from gaseous, liquid and to super-critical during injection. Frequent cavitation and the state change make DME a poor spray penetration characteristics at high engine speed and load.

MTBE for Improved Diesel Combustion and Emissions

Reduced emissions from the spark-ignition engine, when fueled by gasoline containing small amounts of MTBE, have led us to explore similar positive results in compression-ignition (CI) engine combustion by adding this oxygenate compound to Diesel fuel. This study was performed in two separate laboratories by employing the respective experimental apparatus. When a pre-chamber type CI engine was operated by using Diesel fuel mixed with several volume portions of MTBE, including 5, 10 and 15%, several positive results were obtained, as compared with those from the baseline neat Diesel-fueled operations: (1) The engine delivers overall comparable or better performance characteristics: (2) The brake thermal efficiency is higher at the advanced and late injection times; (3) Some considerable reduction of both soot and NOx emissions is found; (4) The ignition delay increases but the combustion duration decreases. In order to help explain the unexpected responses of CI combustion to the above fuel modifications, high-speed in-cylinder spectral infrared digital imaging was performed for the same fuel modification. Some plausible and consistent results are observed, which help explain the above findings. 5 refs., 9 figs.

A Study of S.I. Engine Operated with Oxygen Enriched Air. Unburned Hydrocarbon Characteristics during Warming-up.

Effects of the intake air oxygen enrichment (IOE) on unburned hydrocarbon emissions during the warm-up period in a spark ignition engine were investigated. Hydrocarbon species from C1 to C6, as well as total hydrocarbon concentrations, were determined by gas-chromatography. As a result, the warm-up period of IOE operation was reduced to one third, and hydrocarbon emissions, such as ethylene and benzene, reduced by 90% compared with normal air operation. It was also found that the effect of the decrease in quenching area with IOE on the reduction in hydrocarbon emissions was relatively small.

Compression ignition engine using composite emulsified fuel. Engine performances and combustion characteristics under transient operation.

Transient engine performance, fuel injection and combustion characteristics of prechamber-type compression ignition engines operated with a composite emulsified fuel (composed of gas oil, water and methanol) were investigated. As a result, response of engine speed of composite fuel operation was found to be the same as the gas-oil operation. However, The start of injection timing under transient running was slower than that of steady-state operation. The retarded and fluctuated start of injection timing was caused by the vibration of the pump axis under transient running and the unstable air content of a composite fuel. Therefore the retarded and fluctuated start of injection timing increased the ignition lag and its fluctuation.

The engine performances and exhaust gas characteristics of methanol-fueled two-cycle engines.

The engine performances and exhaust gas characteristics of methanol-fueled two-cycle engines were investigated. The operating conditions such as engine speed, ignition time, throttle valve opening, air fuel ratio, and compression ratio were widely varied to operate the carbureted methanol engine. Furthermore, the electric-controlled fuel injection nozzle which is installed at the scavenging port was employed to operate the methanol engine. As a result, at the operating field of high engine speed and lean mixture, the brake thermal efficiency with the best ignition time of the two-cycle engine was compared with that of a four-cycle engine, and at the above-mentioned operating conditions, the combustion variations and the harmful exhaust emissions of the two-cycle methanol engine showed relatively low levels.