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Homogeneous Charge Compression Ignition (HCCI) combustion has attracted much interest as a combustion system that can achieve both low emissions and high efficiency. But the operating region of HCCI combustion is narrow, and it is difficult to control the auto-ignition timing. This study focused on the use of a two-component fuel blend and supercharging. The blended fuel consisted of dimethyl ether (DME), which has attracted interest as alternative fuel for compression-ignition engines, and methane, the main component of natural gas. A spectroscopic technique was used to measure the light emission of the combustion flame in the combustion chamber in order to ascertain the combustion characteristics. HCCI combustion characteristics were analyzed in detail in the present study by measuring this light emission spectrum.

In this study, experiments were conducted using a blend of two types of fuel with different ignition characteristics. One was dimethyl ether (DME) that has a high cetane number, autoignites easily and displays low-temperature oxidation reaction mechanisms; the other was methane that has a cetane number of zero and does not autoignite easily. A mechanically driven supercharger was provided in the intake pipe to adjust the intake air pressure. Moreover, flame light in the combustion chamber was extracted using a system for observing light emission that occurred in the space between the cylinder head and the cylinder and in the bore direction of the piston crown. The results of previous studies conducted with a supercharged HCCI engine and a blended fuel of DME and methane have shown that heat release of the hot flame is divided into two stages and that combustion can be moderated by reducing the peak heat release rate (HRR).

This study examined the effects of fuel composition and intake pressure on two-stage high temperature heat release characteristics of a Homogeneous Charge Compression Ignition (HCCI) engine. Light emission and absorption spectroscopic measurement techniques were used to investigate the combustion behavior in detail. Chemical kinetic simulations were also conducted to analyze the reaction mechanisms in detail. Blended fuels of dimethyl ether (DME) and methane were used in the experiments. It was found that the use of such fuel blends together with a suitable intake air flow rate corresponding to the total injected heat value gave rise to two-stage heat release behavior of the hot flame, which had the effect of moderating combustion. The results of the spectroscopic measurements and the chemical kinetic simulations revealed that the main reaction of the first stage of the hot flame heat release was one that produced CO from HCHO.

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.

Dimethyl ether(DME) is a promising new alternative fuel not only diesel fuel but also power generation, fuel cell and city gas. However, the 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 is not the liquid spray but similar to that of gas spray. The spray formation is strongly affected by the fuel flow in the nozzle. The Computational Fluid Dynamics (CFD) and the experiments are examined to analyze the fuel flow in the nozzle. The DME physical properties make some difference of the flow in the nozzle, comparing with those of diesel. As a CFD result, cavitation in the injection nozzle is more frequent with DME than with diesel oil.