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The purpose of this study is to operate the spark ignition engine by the dual combustion cycle. The dual combustion cycle has two combustion processes, these are the constant volume combustion and the constant pressure combustion. The lean combustion and the direct fuel injection were applied to realize the dual combustion cycle for spark ignition engines. The combustion of lean mixture was corresponding to the constant volume combustion. The fuel was directly injected to combustion chamber and was burned with the remained oxygen after the lean combustion, so that this was corresponding to the constant pressure diffusion combustion. The combustion experiments were conducted by using the constant volume vessel. The lean propane-air mixture of which equivalence ratios were 0.6, 0.7, 0.8 and 0.9 were used and liquid n-heptane was injected by using the high-voltage electrical discharge.

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.

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.

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 realize dual-combustion cycle for gasoline engines. For the purpose, lean combustion and direct fuel injection were applied to small diesel engine. The lean gasoline-air mixture was provided and was ignited by small amount of pilot diesel fuel injection (constant volume combustion). Then, diesel fuel was injected by main injection and was burned with the remained oxygen after the lean combustion (diffusion combustion). The equivalence ratio 0.3, 0.4 and 0.5 of mixture were used to avoid the spontaneous compression auto-ignition. The total equivalence ratio with supplied gasoline and diesel fuel was adjusted to 1.0. The base pilot injection timing was selected as the ignition of pre-mixture took place at T.D.C. and pilot injection timings were changed 2 degree before and behind of base timing. The main fuel injection timings were 50, 75 and 100% of the duration between pilot injection timing and T.D.C.

Although methane number is widely used to predict knocking occurrence and its intensity, it does not determine a fuel composition uniquely, that means, the knocking intensity by the different composition fuel must show difference even if the same methane number fuels are employed. To establish a novel index, the knocking intensity and the autoignitive propagation velocity, as consequence of spontaneous ignition process, are investigated both experimentally and numerically by using the different composition gaseous fuels with same methane number. Methane/ethane/air and methane/n-butane/air mixtures with the same methane number of 70 and the equivalence ratio of 0.5 were employed. They are rapidly compressed and ignited spontaneously by a Rapid Compression Machine. Ignition delay times, autoignitive propagation velocities, and knocking intensity were measured by acquired pressure histories and high-speed imaging.

This study investigated the influence of EGR and spark advance on knocking under high compression ratio, ultra-lean mixture and supercharged condition using premium gasoline as a test fuel. A high-compression ratio, supercharged single cylinder engine was used in this experiment. As a result, the period from ignition to autoignition was prolonged. In addition, knock intensity was drastically reduced. In other words, it is inferred that by combining an appropriate amount of EGR and spark advance, high efficiency operation avoiding knocking can be realized.

The uniform lean gasoline-air mixture was provided to diesel engine and was ignited by direct diesel fuel injection. The mixing region that is formed by diesel fuel penetration and entrainment of ambient mixture is regarded as combustible turbulent jet. The ignition occurs in this region and the ambient lean mixture is burned by flame propagation. The lean mixture of air-fuel ratio between 150 and 35 could be ignited and burned by this ignition method. An increase of diesel fuel injection is effective to ensure combustion and ignition. As diesel fuel injection increases, HC concentration decreases, and NOx and CO concentration increases.

A small 2-stroke engine can be an effective power source for an electric generator mounted on a series hybrid electric vehicle. In recent years, a technology referred to as pre-chamber jet combustion has attracted attention as a means of enhancing thermal efficiency by improving mixture ignitability. In this study, experiments were conducted to investigate differences in combustion behavior between the application of spark-ignited (SI) combustion and pre-chamber jet combustion to a small, two-stroke engine. The experimental equipment used was a two-stroke, single-cylinder, optically accessible engine with a displacement of 63.3 cm3. Differences between conventional SI combustion and pre-chamber jet combustion were examined by means of in-cylinder pressure analysis, in-cylinder combustion visualization and image processing software. The diameter of the connecting orifice of the pre-chamber was varied between two types.

The aim of this research was to investigate the mechanism causing autoignition and the effect of exhaust gas recirculation (EGR) on combustion by detecting the behavior of the OH radical and other excited molecules present in the flame in a spark ignition engine. The test equipment used was a 2-cycle engine equipped with a Schnürle scavenging system. Using emission spectroscopy, the behavior of the OH radical was measured at four locations in the end zone of the combustion chamber. The OH radical plays an important role in the elemental reactions of hydrocarbon fuels. When a certain level of EGR was applied according to the engine operating conditions, the unburned gas became active owing to heat transfer from residual gas near the measurement positions on the exhaust port side and the influence of excited species in the residual gas, and autoignition tended to occur.

The study deals with the light absorption and emission behavior in the preflame reaction interval before hot flame reactions.(1-3) Absorption spectroscopy was used to measure the behavior of HCHO and OH radicals during a progression from normal combustion to knocking operation. Emission spectroscopic measurements were obtained in the same way that radical added HCO. Radical behavior in preflame reactions was thus examined on the basis of simultaneous measurements, which combined each absorption wavelength with three emission wavelength by using a monochromator and a newly developed polychromator.(4-5) When n-heptane (0 RON) and blended fuel (50 RON) were used as test fuel, it was observed that radical behavior differed between normal combustion and knocking operation and a duration of the preflame reaction was shorter during the progression from normal combustion to a condition of knocking.

In plasma jet ignition, combustion enhancement effects are caused toward the plasma jet issuing direction. Therefore, when the igniter is attached at the center of cylindrically shaped combustion chamber, the plasma jet should issues toward the round combustion chamber wall. The plasma jet igniter that had a concentric circular orifice has been developed. It is expected that the plasma jet is issued and is diffused from concentric circular orifice toward the combustion chamber wall. Relationship between plasma jet and igniter configuration was experimentally clarified. Plasma jet can issue from the entire concentric circular orifice for some igniter. Plasma jet is extended with increasing concentric circular orifice area. Plasma jet penetration increases with increasing concentric circular orifice width.

Suppression or reduction of soot emissions is an important goal in the development of automotive engines for environmental and human health purposes. A better understanding at the molecular level of the formation process of soot particles resulting from collision and aggregation of smaller particles made of Polycyclic Aromatic Hydrocarbon (PAH) is needed. In addition to experiments, computational methods are efficient and valuable tools for this purpose. As a first step in our detailed computational chemistry study, we applied Ultra-Accelerated Molecular Dynamics (UAQCMD) and Canonical Monte-Carlo (CMC) methods to investigate the nucleation process. The UA-QCMD can calculate chemical reaction dynamics 107 times faster than conventional first principle molecular dynamics methods, while CMC can calculate equilibrium properties at various temperatures, pressures, and chemical compositions.

In this study, optical measurements were made of the combustion chamber gas during operation of a Homogeneous Charge Compression Ignition (HCCI) engine in order to obtain a better understanding of the ignition and combustion characteristics. The principal issues of HCCI engines are to control the ignition timing and to optimize the combustion state following ignition. Autoignition in HCCI engines is strongly influenced by the complex low-temperature oxidation reaction process, alternatively referred to as the cool flame reaction or negative temperature coefficient (NTC) region. Accordingly, a good understanding of this low-temperature oxidation reaction process is indispensable to ignition timing control. In the experiments, spectroscopic measurement methods were applied to investigate the reaction behavior in the process leading to autoignition.

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.

In this study, light emission and absorption spectroscopic measurement techniques were used to investigate the Homogeneous Charge Compression Ignition (HCCI) combustion process in detail, about which there have been many unclear points heretofore. The results made clear the formation behavior and wavelength bands of the chemical species produced during low-temperature reactions. Specifically, with a low level of residual gas, a light emission band was observed from a cool flame in a wavelength range of 370–470 nm. That is attributed to the light emission of formaldehyde (HCHO) produced in the cool-flame reactions. Additionally, it was found that these light emission spectra were no longer observable when residual gas was applied. The light emission spectra of the combustion flame thus indicated that residual gas has the effect of moderating cool-flame reactions.

We developed a novel ignition method called laser breakdown-assisted long-distance discharge ignition (LBALDI) that combines laser breakdown with a discharge to realize lean combustion. The creation of laser breakdown plasma between electrodes for discharge enables discharges over longer distances than those of conventional sparkplug as inferred from laser-triggered lightning or laser-triggered gas switches. This method should help realize volumetric ignition through the creation of a long-distance discharge. Experiments on the fundamental discharge and ignition of methane/air mixtures were conducted. The optimum incident time of the laser prior to the application of a high voltage was found to reduce the sparkover voltage and markedly reduce the voltage required by LBALDI under pressurized air conditions. In the ignition experiment, LBALDI showed the fastest heat release rate at the lean flammable limit.

This study focused on a lean-burn regime using a pre-chamber for improving the efficiency of internal combustion engines. Combustion images were visualized using a two-stroke, single-cylinder, optically accessible engine fitted with a cylindrical pre-chamber. The L/D ratio of the pre-chamber length (L) to its diameter (D) and the diameter of the pre-chamber orifice were varied as parameters. Combustion characteristics were analyzed based on the visualized jet flow configuration and combustion chamber pressure measurements. The results revealed that the combustion duration tended to be longer with a smaller L/D ratio and that the coefficient of variation (COV) of the indicated mean effective pressure (IMEP) was smaller and more stable. With a smaller orifice diameter, the jet velocity was faster, and the flame development duration was shorter, but the combustion duration was longer; IMEP tended to be lower, but the COV of IMEP was smaller.

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.

A Spark Ignition Engine has some kinds of problem to be solved over many years, one of them is abnormal combustion; Low-speed pre-ignition (LSPI) under low-speed, high-load driving conditions for vehicle, and pre-ignition under longterm operation without cleaning a combustion chamber for gas cogeneration. As a cause for abnormal combustion, engine oil droplets diluted by liquid fuel and peeled combustion deposits delivered from engine oil are proposed. In this study, experiments were conducted focusing on engine oil additives having different chemical structure and abnormal combustion behavior. A four-stroke side-valve single cylinder engine that allowed in-cylinder visualization of the combustion flame was used in the experiments. The experimental results showed that the influence of DTC additive on abnormal combustion is small and the zinc component contained in the DTP additives had the effect of advancing the autoignition timing.