Search Results

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 focused on the use of a two-component fuel blend and supercharging as possible means of overcoming these issues of HCCI combustion. Low-carbon gaseous fuels with clean emissions were used as the test fuels. The specific fuels used were dimethyl ether (DME, cetane number of 55 or higher) that autoignites easily And exhibits pronounced low-temperature oxidation reactions, methane (cetane number of 0) that does not autoignite readily and is the main component of natural gas which is regarded as petroleum substitute, and propane (cetane number of 5) that is a principal component of liquefied petroleum gas. The results of previous investigations have shown that the use of a blended fuel of DME and methane produces a two-stage main combustion process under certain operating conditions, with the result that combustion is moderated.

This study clarified the influence of hot gas jet on combustion enhancement effect for lean mixture in the plasma jet ignition. The hot gas jet was generated by the high temperature plasma and was ejected from igniter after plasma jet finished issuing. In combustion tests, propane-air mixture at equivalence ratio of 0.6 was used and the mixture was filled in the combustion chamber at atmosphere pressure and room temperature. For generation of the hot gas jet, the standard air was filled in chamber at same conditions and the hot gas jet was visualized by schlieren method in the absence of combustion. The combustion development processes were also visualized and the combustion pressure was measured. The discharge voltage, discharge current and the plasma luminescence were also measured. The plasma luminescence disappeared within 0.05 ms for any experimental conditions. When cavity depth was deep and orifice diameter was small, the maximum plasma luminescence height was short.

Attention has recently been focused on homogeneous charge compression ignition (HCCI) as an effective combustion process for resolving issues inherent to the nature of combustion. Dimethyl ether (DME; CH3OCH3) has attracted interest as a potential alternative fuel for compression ignition engines. We measured the HCCI process of DME in a test diesel engine by using a spectroscopic method. Simultaneous measurements were also done on exhaust emissions of hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx). Based on the experimental data, this paper discusses the relationship between the equivalence ratio and the observed tendencies.

Homogeneous Charge Compression Ignition (HCCI) combustion has attracted widespread interest as a combustion system that offers the advantages of high efficiency and low exhaust emissions. However, it is difficult to control the ignition timing in an HCCI combustion system owing to the lack of a physical means of initiating ignition like the spark plug in a gasoline engine or fuel injection in a diesel engine. Moreover, because the mixture ignites simultaneously at multiple locations in the cylinder, it produces an enormous amount of heat in a short period of time, which causes greater engine noise, abnormal combustion and other problems in the high load region. The purpose of this study was to expand the region of stable HCCI engine operation by finding a solution to these issues of HCCI combustion.

Issues that must be addressed to make Homogeneous Charge Compression Ignition (HCCI) engines a practical reality include the difficulty of controlling the ignition timing and suppression of rapid combustion under high load conditions. Overcoming these issues to make HCCI engines viable for practical application is indispensable to the further advancement of internal combustion engines. Previous studies have reported that the operating region of HCCI combustion can be expanded by using DME and Methane blended fuels.(1), (2), (3), (4), (5) The reason is that the reaction characteristics of these two low-carbon fuels, which have different ignition properties, have the effect of inducing heat release in two stages during main combustion, thus avoiding excessively rapid combustion. However, further moderation of rapid combustion in high-load region is needed to expand the operation region. This study focused on supercharging and use of blended fuels.

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.

In this study, a spectroscopic method was used to measure the combustion characteristics of a test diesel engine when operated on dimethyl ether (DME) under a homogenous charge compression ignition (HCCI) combustion process. A numerical analysis was made of the elementary reactions using Chemkin 4.0 to perform the calculations. The results of the analysis showed that compression ratio changes and the methane additive influenced the autoignition timing in the DME-HCCI combustion process. In the experiments, reducing the compression ratio delayed the time of the peak cylinder pressure until after top dead center, thereby increasing the crankshaft output and thermal efficiency. The addition of methane enabled the DME-HCCI engine to provide crankshaft output equivalent to that seen for diesel engine operation at a low equivalence ratio. This paper discusses these effects in reference to the experimental and calculated results.

In this research, the effect of high-temperature residual gas, resulting from the application of a certain level of EGR, on combustion was investigated using a two-stroke engine and alcohol fuels (ethanol and methanol) and gasoline as the test fuels. Measurements were made of the light emission intensity of the OH radical on the intake and exhaust port sides of the combustion chamber and of the combustion chamber wall temperature (spark plug washer temperature) and the exhaust gas temperature. Data were measured and analyzed in a progression from normal combustion to autoignited combustion to preignition and to knocking operation.

Homogeneous Charge Compression Ignition (HCCI) has attracted a great deal of interest as a combustion system for internal combustion engines because it achieves high efficiency and clean exhaust emissions. However, HCCI combustion has several issues that remain to be solved. For example, it is difficult to control engine operation because there is no physical means of inducing ignition. Another issue is the rapid rate of heat release because ignition of the mixture occurs simultaneously at multiple places in the cylinder. The results of previous investigations have shown that the use of a blended fuel of DME and propane was observed that the overall combustion process was delayed, with that combustion became steep when injected propane much. This study focused on expanding the region of stable engine operation and improving thermal efficiency by using supercharging and blended fuels. The purpose of using supercharging were in order to moderated combustion.

In this study, a detailed analysis was made of supercharged HCCI combustion using a two-component fuel blend of dimethyl ether (DME), which has attracted interest as a potential alternative fuel, and methane. The quantity of fuel injected and boost pressure were varied to investigate the equivalence ratio and operating region conducive to optimal HCCI combustion. The results revealed that varying the boost pressure according to the engine load and applying a suitable equivalence ratio induced two-stage main combustion over a wide load range, making it possible to avoid excessively rapid combustion.

In this study, the effect of corona discharge on the combustion phenomenon has been made clear. A homogeneous propane-air mixture was used and six equivalence ratios were tested. For generating the positive and negative corona discharge, a non-uniform electric field was applied to the combustion chamber by the needle to plane gap. One or five needle-shaped electrodes were used to change the corona discharge state. When the positive corona discharge was applied, the luminescence from corona with five electrodes was weak as compared with that of one needle-shaped electrode. When the negative corona discharge was applied, the luminescence from corona and combustion were not affected by the number of electrode. When the positive corona discharge was applied by low voltage, the combustion was improved in the case of one needle-shaped electrode, but the index of combustion with one needle-shaped electrode was almost equal to that of five electrodes when the high voltage was applied.

Attention has recently been focused on homogeneous charge compression ignition combustion (HCCI) as an effective combustion process for resolving the essential nature of combustion. Meanwhile, dimethylether (DME) has attracted interest as a potential alternative fuel for compression ignition engines. Authors measured the combustion process of DME HCCI by using a spectroscopic method. A diesel engine was used as the test engine. The results of these analyses showed that changes in the compression ratio, intake air temperature and equivalence ratio influenced the ignition timing in the HCCI combustion process. This paper discusses these effects in reference to the experimental and calculated results.

The purpose of this study is to elucidate the development process of hot kernel generated by the laser induced breakdown and to clarify the relationship between corona discharge application and flame propagation. The mixture can be ignited by the laser induced breakdown. Nd:YAG laser is used for the ignition and laser light is optically focused on the central part of combustion chamber by a plano convex lens. The hot kernel is observed in the absence of combustion and is rapidly developed into the laser incidence side. The homogeneous propane-air mixture is used and six equivalence ratios between 0.7 and 1.5 are tested. For generating the positive corona discharge in the combustion chamber, a non-uniform electric field is applied by the needle to plane gap. In a lean mixture, the whole flame front shifts to downward from the breakdown point and, in the rich mixture region, the combustion is strongly enhanced.

The new fuel injection method which is using the high-voltage electrical discharge has been proposed. The plasma jet ignition technology is applied to this injection system, and the component parts of fuel injector are similar to the plasma jet igniter. The purpose of this study is to elucidate the spray characteristics and the fuel injection development processes of this injection method. To obtain the influence of injector configuration and supplied electrical discharge energy on the fuel spray, the fuel is ejected into the open atmosphere and fuel injection development process is visualized by the schlieren method. The penetration depth, maximum width and projected area of fuel spay increase with increasing in the electrical discharge energy and an orifice diameter. In the case at which the large electrical discharge energy is provided, the fuel injection is finished within a short duration and the mean fuel spray velocity becomes fast.

The composition ratio of saturated and unsaturated fatty acid methyl esters (FAME) is depended on feedstock. Three FAMEs: soybean (SME), palm (PME) and coconut oil (CME) methyl esters were mixed to make fuels which have different composition ratio. The ignitability of fuel which mainly consisted of unsaturated FAME was inferior. Power was slightly reduced with increasing of mixing ratio of CME; however exhaust gas emissions were improved because CME contained a lot of oxygen atoms. Fuel which was equal mixture SME and CME indicated almost the same ignition characteristic as that of PME because they have same composition ratio.

The Homogeneous Charge Compression Ignition (HCCI) engine has attracted much interest in recent years because it can simultaneously achieve high efficiency and low emissions. However, it is difficult to control the ignition timing with this type of engine because it has no physical ignition mechanism. Varying the amount of fuel supplied changes the operating load and the ignition timing also changes simultaneously. The HCCI combustion process also has the problem that combustion proceeds too rapidly. This study examined the possibility of separating ignition timing control and load control using an HCCI engine that was operated on blended test fuels of dimethyl ether (DME) and methane, which have vastly different ignition characteristics. The influence of the mixing ratios of these two test fuels on the rapidity of combustion was also investigated.

There are few investigations to change wood biomasses to the industrially available energy, so that a new conversion technology of biomass to liquid fuel has been established by the direct liquefaction process. However, cellulosic liquefaction fuel (for short CLF) cold not mixed with diesel fuel. In this study, the plastic was mixed with wood to improve the solubility of CLF to diesel fuel. CLF made by the direct co-liquefaction process could be stably and completely mixed with diesel fuel in any mixing ratio and CLF included 2 wt.% of oxygen. The test engine was an air-cooled, four-stroke, single cylinder, direct fuel injection diesel engine. In the engine starting condition test, the ignition timing of 5 wt.% CLF mixed diesel fuel was slightly delayed at immediately after the engine started, however the ignition timing was almost the same as diesel fuel after the engine was warmed-up.

The flame propagation behavior of homogeneous hydrogen-air mixture under application of high-voltage uniform or non-uniform electric field was explored by using combustion vessel. When a uniform electric field was applied, two plate electrodes were attached to ceiling and bottom of combustion chamber and, to apply a non-uniform electric field, an electrode in ceiling was needle-shaped and an electrode in bottom was plate-shaped. The positive or negative polarity DC high voltage was applied for an electrode in ceiling. When a positive polarity non-uniform electric field was applied to the mixture at any equivalence ratios and the input voltage was higher than 12 kV, the flame propagation was enhanced in the downward direction. This is because the corona wind was generated from the tip of needle-shaped electrode to grounded electrode by the brush corona.