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Bio-ethanol is one of the candidates for automotive alternative fuels. For reduction of carbon dioxide emissions, it is important to investigate its optimum combustion procedure. This study has explored effect of ethanol fuels on HCCI-SI hybrid combustion using dual fuel injection (DFI). Steady and transient characteristics of the HCCI-SI hybrid combustion were evaluated using a single cylinder engine and a four-cylinder engine equipped with two port injectors and a direct injector. The experimental results indicated that DFI has the potential for optimizing ignition timing of HCCI combustion and for suppressing knock in SI combustion under fixed compression ratio. The HCCI-SI hybrid combustion using DFI achieved increasing efficiency compared to conventional SI combustion.

It is important in the application of bio-ethanol in homogeneous-charge compression ignition (HCCI) engines to investigate the HCCI combustion characteristics of ethanol. As the inhibitory mechanism of ethanol on HCCI combustion is a key factor, simulated chemical reactions are necessary. In this study, chemical reaction simulations in the combustion chamber of a rapid compression machine (RCM) were performed in order to investigate the inhibitory mechanism of ethanol on the HCCI combustion of heptane. The sensitivity analysis results suggested that the OH radical consumption reaction by ethanol that occurs would inhibit the cool flame reaction of heptane. Furthermore, visualization of HCCI combustion with the RCM was conducted using a quartz glass combustion chamber head and ICCD camera. As a result, the cool flame luminescence intensity of heptane was reduced by the addition of ethanol.

For the purpose of developing onboard gasoline reforming technology for higher octane number fuel on demand, octane number enhancement of gasoline surrogate by aerobic oxidation using N-hydroxyphthalimide catalyst was investigated. At first, octane numbers of the oxygen-containing products from alkane and aromatic compound were estimated using a fuel ignition analyzer. As a result, not only alcohol but also ketones and aldehydes have higher octane numbers than the original alkanes and aromatic compound. Next, gasoline surrogate was oxidized aerobically with N-hydroxyphthalimide derivative catalyst and cobalt catalyst at conditions below 100 °C. As a result, fuel molecules were oxidized to produce alcohols, ketones, aldehydes, and carboxylic acids. N-hydroxyphthalimide derivative catalyst with higher solubility in gasoline surrogate has higher oxidation ability. Furthermore, the estimated octane number of the oxidized gasoline surrogate improves 17 RON.

It is known that lean combustion is effective as one of the ways which improves thermal efficiency of a gasoline engine. In the interest of furthering efficiency, the use of leaner mixtures is desired. However, to realize robust lean combustion it is necessary to reduce combustion cyclic variation while managing the emission nitrogen oxides. In this study, combustion analysis was carried out focusing on cyclic variations of the heat release of lean combustion. Since the initial flame kernel growth speed has a great effect on the indicated mean effective pressure, laminar flame speed (LFS) around the spark plug was analyzed. Infrared absorption spectrophotometry was used for the measurement of a fuel concentration around the spark plug. Moreover, a LFS predicting formula, which can be used in an area leaner than before, was drawn from detailed chemical reaction calculation results, and the LFS around the spark plug was also calculated through the use of this formula.

Compression ignition combustion with a lean mixture has high potential in terms of high theoretical thermal efficiency and low NOx emission characteristics due to low combustion temperatures. In particular, a Dual-Fuel concept is proposed to achieve high ignition timing controllability and an extended operation range. This concept controls ignition timing by adjusting the fraction of two fuels with different ignition characteristics. However, a rapid combustion process after initial ignition cannot be avoided due to the homogenous nature of the fuel mixture, because the combustion process depends entirely on the high reaction rate of thermal ignition. In this study, the effect of mixture stratification in the cylinder on the combustion process after ignition based on the Dual-Fuel concept was investigated. Port injection of one fuel creates the homogeneous mixture, while direct injection of the other fuel prepares a stratified mixture in the cylinder at the compression stroke.

In practical lean burn engines used to date, the use of a stratified air-fuel configuration, with a comparatively rich mixture in the vicinity of the spark plugs, has resulted in the stable combustion of an overall lean mixture. However, because a comparatively rich mixture is burned during the first half of combustion, NOx emissions are not reduced sufficiently. This research focused on a form of lean burn with homogeneous premixture that would be able to balance low NOx emissions with combustion controllability. It is widely known that homogeneous lean premixed gas has poor flame propagation characteristics. To determine the dominant cause of this, this study investigated the combustion properties of a single-cylinder engine while changing the compression ratio and intake temperature. As a result, the primary cause of combustion fluctuation, the abnormal cycle has a low TDC temperature compared to that of other cycles.

Gasoline includes various kinds of chemical species. Thus, the reaction model of gasoline components that includes the low-temperature oxidation and ignition reaction is necessary to investigate the method to control the combustion process of the gasoline engine. In this study, a gasoline combustion reaction model including n-paraffin, iso-paraffin, olefin, naphthene, alcohol, ether, and aromatic compound was developed. KUCRS (Knowledge-basing Utilities for Complex Reaction Systems) [1] was modified to produce paraffin, olefin, naphthene, alcohol automatically. Also, the toluene reactions of gasoline surrogate model developed by Sakai et al. [2] including toluene, PRF (Primary Reference Fuel), ethanol, and ETBE (Ethyl-tert-butyl-ether) were modified. The universal rule of the reaction mechanisms and rate constants were clarified by using quantum chemical calculation.