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Hydrogen produced from regenerative sources has the potential to be a sustainable substitute for fossil fuels. A hydrogen internal combustion engine has good combustion characteristics, such as higher flame propagation velocity, shorter quenching distance, and higher thermal conductivity compared with hydrocarbon fuel. However, storing hydrogen is problematic since the energy density is low. Hydrogen can be chemically stored as a hydrocarbon fuel. In particular, an organic hydride can easily generate hydrogen through use of a catalyst. Additionally, it has an advantage in hydrogen transportation due to its liquid form at room temperature and pressure. We examined the application of an organic hydride in a spark ignition (SI) engine. We used methylcyclohexane (MCH) as an organic hydride from which hydrogen and toluene (TOL) can be reformed. First, the theoretical thermal efficiency was examined when hydrogen and TOL were supplied to an SI engine.

For better understanding of the in-cylinder combustion characteristics of DME, combustion radicals of a direct injection DME-Fueled compression ignition engine were observed using a spectroscopic method. In this initial report, the emission intensity of OH, CH, CHO, C2 and NO radicals was measured using a photomultiplier. These radicals could be measured with wavelength resolution (half-width) of about 3.3 nm. OH and CHO radicals appeared first, and then CH radical emission was detected. After that, the combustion radicals were observed using a high-speed image intensified video camera. C2 and CH radicals were able to observe roughly as images. However, the emission intensity of DME combustion was not strong enough to take OH, CHO and NO radical images. CH radical combustion occurred near the chamber wall and burned like a ring, as combustion progress, indicating active heat release occurred near the chamber wall.

Dimethyl Ether (DME) is one of the major candidates for the next generation fuel for compression ignition (CI) engines. It has good self-ignitability and would not produce particulate, even at rich conditions. DME has proved to be able to apply to ordinary diesel engines with minimal modifications, but its combustion characteristics are not completely understood. In this study, the behavior of a DME spray and combustion process of a direct injection CI engine fueled with DME was investigated by combustion observation and in-cylinder gas sampling. To distinguish evaporated and non-evaporated zones of a spray, direct and schlieren imaging were carried out. The sampled gas from a DME spray was analyzed by gas chromatography, and the major intermediate product histories during ignition period were analyzed.

This research investigated the performance and emissions of a direct injection (DI) Diesel engine operated on 100% butane liquid petroleum gas (LPG). The LPG has a low cetane number, therefore di-tertiary-butyl peroxide (DTBP) and aliphatic hydrocarbon (AHC) were added to the LPG (100% butane) to enhance cetane number. With the cetane improver, stable Diesel engine operation over a wide range of the engine loads was possible. By changing the concentration of DTBP and AHC several different LPG blended fuels were obtained. In-cylinder visualization was also used in this research to check the combustion behavior. LPG and only AHC blended fuel showed NOX emission increased compared to Diesel fuel operation. Experimental result showed that the thermal efficiency of LPG powered Diesel engine was comparable to Diesel fuel operation. Exhaust emissions measurements showed that NOX and smoke could be considerably reduced with the blend of LPG, DTBP and AHC.

Based on the knowledge that cavitation in a nozzle enhances the atomization of fuel spray, fuel modification is conducted by blending Dimethyl Ether (DME). Because the boiling point of DME is -24.8°C, it may easily take place during the cavitation in an injection nozzle. Furthermore, there is a soot reduction effect caused by the oxygenated fuels. The oxygen content in the DME is 34.8%, which accelerates soot reduction in the combustion chamber. The experimental results are compared with those of DiMethoxyMethan (Methylal: DMM), a blend of gas-oil. The ignition temperatures of DME and DMM are 235°C and 236°C, the boiling temperatures of DME and DMM are -24.8°C and 42.1°C, and the oxygen contents of DME and DMM are 34.8% and 42.1%, respectively. In addition to the oxygenated fuel, a propane blend of gas-oil was also used as a blended fuel in order to examine the effects of the boiling point and oxygen content of the fuel.

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.

A direct fuel-injection two-stroke cycle engine operated with neat methanol was investigated. The engine performance, combustion and exhaust-gas characteristics were analyzed experimentally and compared for operation with a carburetor, EFI injection at the intake manifold, and EFI injection at the scavenging port. The power and the brake thermal efficiency of the direct fuel-injection engine were higher than those of engines operated with a carburetor and either of the two EFI methods. The exhausted unburnt fuel of the direct fuel-injection engine was lower than that for operation with a carburetor, and formaldehyde and the CO concentration were of the same level as for operation with the carburetor and EFI methods. The NOx concentration of the direct fuel-injection was half the level of the result of carburetor operation.

A water/Oil type emulsified fuel has been demonstrated to decrease the harmful exhaust emissions and increase a thermal efficiency of internal combustion engine experimentally(1)*. However, an emulsified fuel is not currently used for internal combustion engines. When we try to use an emulsified fuel for the internal combustion engines, especially for a compression ignition engine, we should clear the physical properties of emulsified fuel. Because the viscosity of the emulsified fuel affects the spray characteristics and following combustion characteristics. It is commonly recognized that the viscosity of emulsified fuel is much higher than that of the base fuels. However, there are no data which show the viscosity increase of emulsified fuel. We proposed an newly introduced specific surface area Sp/Se to estimate the viscosity of the emulsified fuel.

Under accelerating or decelerating operation, it is demanded to improve the performance and to reduce the exhaust smoke of diesel engines. Regarding the exhaust smoke regulation for a vehicle engine under transitional operation, the so-called free or controlled accelerating operation, are adopted as the simple measuring method. And the engine applied the construction or agricultural use is always operating under the load conditions of stepwise or periodical changes. For two-stroke cycle engines, in particular, the effects of operating conditions on the engine performance and the smoke character are unclear. In order to meet such demand, it is necessary to make clear the transitional character of each transfer element, i.e., the fuel injection system, the combustion process and the frictional loss.