Search Results

In this study, the heated fuels were provided to the diesel engine in order to activate the fuel before the injection. Two test fuels: the normal diesel fuel and cetane, which have different boiling points were used. For both normal diesel fuel and cetane, crank angles at ignition and maximum pressure are delayed and the maximum combustion pressure is decreased as the fuel temperature rises. In cases of large and middle mass flow rate of fuel injection, the brake thermal efficiency and brake mean effective pressure are decreased when the fuel temperature is higher than 570 [K]. However, in the case of small mass flow rate of fuel injection, the brake thermal efficiency is almost independent of fuel temperature. HC and CO concentrations in the exhaust gas emission show constant values regardless of fuel temperature. However, NOx concentration is gradually decreased as the fuel temperature rises.

The growing severity of global environmental issues in recent years, including air pollution and the depletion of fossil fuels, has made it necessary for internal combustion engines to achieve higher efficiency and lower exhaust emission levels. Calls for reducing atmospheric emissions of carbon dioxide (CO₂) necessitate thoroughgoing measures to lower the levels of CO₂ originating in the combustion process of internal combustion engines and to facilitate operation on diverse energy sources. Homogeneous Charge Compression Ignition (HCCI) combustion has attracted widespread interest because it achieves high efficiency and can reduce particulate matter (PM) and nitrogen oxide (NOx) emissions simultaneously. These characteristics are obtainable because HCCI combustion can take place at ultra-lean conditions exceeding the limits of flame propagation.

Internal combustion engines have been required to achieve even higher efficiency in recent years in order to address environmental concerns. However, knock induced by abnormal combustion in spark-ignition engines has impeded efforts to attain higher efficiency. Knock characteristics during abnormal combustion were investigated in this study by in-cylinder visualization and spectroscopic measurements using a four-stroke air-cooled single-cylinder engine. The results revealed that knock intensity and the manner in which the autoignited flame propagated in the end gas differed depending on the engine speed.

The Homogenous Charge Compression Ignition (HCCI) engine is positioned as a next-generation internal combustion engine and has been the focus of extensive research in recent years to develop a practical system. One reason is that this new combustion system achieves lower fuel consumption and simultaneous reductions of nitrogen oxide (NOx) and particulate matter (PM) emissions, which are major issues of internal combustion engines today. However, the characteristics of HCCI combustion can prevent suitable engine operation owing to the rapid combustion process that occurs accompanied by a steep pressure rise when the amount of fuel injected is increased to obtain higher power output. A major issue of HCCI is to control this rapid combustion so that the quantity of fuel injected can be increased for greater power. Controlling the ignition timing is also an issue because it is substantially influenced by the chemical reactions of the fuel.

Lean-burn technology is regarded as one effective way to increase the efficiency of internal combustion engines. However, stable ignition is difficult to ensure with a lean mixture. It is expected that this issue can be resolved by improving ignition performance as a result of increasing the amount of energy discharged into the gaseous mixture at the time of ignition. There are limits, however, to how high ignition energy can be increased from the standpoints of spark plug durability, energy consumption and other considerations. Therefore, the authors have focused on a multistage pulse discharge (MSPD) ignition system that performs low-energy ignition multiple times. In this study, a comparison was made of ignition performance between MSPD ignition and conventional spark ignition (SI). A high-speed camera was used to obtain visualized images of ignition in the cylinder and a pressure sensor was used to measure pressure histories in the combustion chamber.

This study attempted to elucidate combustion conditions in a progression from normal combustion to knocking by analyzing the ion current and light emission intensity that occurred during this transition. With the aim of understanding the combustion states involved, the ion current was measured at two positions in the combustion chamber. Light emission spectroscopy was applied to examine preflame reactions that are observed prior to autoignition in the combustion process of hydrocarbon fuels. The results obtained by analyzing the experimental data made clear the relationship between the ion current and light emission during the transition from normal combustion to knocking operation.

This study investigated the origin of knocking combustion accompanied by pressure wave and strong pressure oscillations in a Homogeneous Charge Compression Ignition (HCCI) engine. Experiments were conducted with a two-stroke single cylinder optically accessible engine that allowed the entire bore area to be visualized. The test fuel used was n-heptane. The equivalence ratio and intake temperature were varied to induce a transition from moderate HCCI combustion to extremely rapid HCCI combustion accompanied by in-cylinder pressure oscillations. Local autoignition and pressure wave behavior under each set of operating conditions were investigated in detail on the basis of high-speed in-cylinder visualization and in-cylinder pressure analysis. As a result, under conditions where strong knocking occurs, a brilliant flame originates from the burned gas side in the process where the locally occurring autoignition gradually spreads to multiple locations.

In-cylinder visualization of the entire bore area at an identical frame rate was used to investigate knocking conditions under spark ignition (SI) combustion and under Homogeneous Charge Compression Ignition (HCCI) combustion in the same test engine. A frequency analysis was also conducted on the measured pressure signals. The results revealed that a combustion regime accompanied by strong pressure oscillations occurred in both the SI and HCCI modes, which was presumably caused by rapid autoignition with attendant brilliant light emission that took place near the cylinder wall. It was found that the knocking timing was the dominant factor of this combustion regime accompanied by cylinder pressure oscillations in both the SI and HCCI combustion modes.

Knocking is one phenomenon that can be cited as a factor impeding efforts to improve the efficiency of spark-ignition engines. With the aim of understanding knocking better, light emission spectroscopy was applied in this study to examine preflame reactions that can be observed prior to autoignition in the combustion reaction process of hydrocarbon fuels. Attention was focused on light emission behavior at wavelengths corresponding to those of formaldehyde (HCHO), Vaidya's hydrocarbon flame band (HCO) and the OH radical in a forced progression from normal combustion to a knocking state. Light emission behavior was measured simultaneously in the center and in the end zone of the combustion chamber when the engine was operated on two different test fuels. The test fuels used were n-heptane (0 RON) and a blended fuel (70 RON) consisting of n-heptane (0 RON) and iso-octane (100 RON).

The purpose of this study is to explore an effect of the coconut oil methyl ester (CME) and vegetable oil methyl ester (VME) on a low compression ratio diesel engine performance. CME and VME were produced from coconut oil and vegetable oil with methanol, respectively. Vegetable oil was assumed to contain 60 wt.% of soybean oil and 40 wt.% rapeseed oil. The engine performance was measured in the steady operating condition at 3600 rpm of engine speed. The ignition timings of CME and VME were advanced and the maximum cylinder pressures of CME and VME were higher as compared with the diesel fuel at low compression ratio, because CME and VME consisted of medium chain fatty acid methyl esters. The ignitability of CME was superior to VME, because CME consisted of saturated fatty acid. The brake thermal efficiency of diesel fuel was slightly higher than CME and VME at any compression ratios.

The purpose of this study is to explore an effect of cooled-EGR on the diesel engine performance fueled with coconut-oil methyl ester (CME). The exhaust gas was cooled by the water at room temperature and was fed to the intake manifold, and the EGR rate was changed from 0 % to 30 % at every 10 %. The engine performances were measured at several EGR rates, fuel injection pressures and timings. Test fuels were CME and commercial diesel fuel. In the case of high EGR rate at which the compression ignition was deteriorated, the ignition timing of CME was always earlier than that of diesel fuel, therefore CME had good ignitability as compared with diesel fuel under EGR application. When the fuel injection pressure was increased at high EGR rate, the ignition delay was improved by the fuel atomization and air-fuel mixing effect.

Recently, it was required that the body should be made lightweight. The use of extrusion aluminum elements as the body frame structure is one way of satisfying the requirement. In this research, the cross-section was designed to optimum shape for the maximum crash energy absorption. The energy absorption is performed by the plastic buckling deformation. Therefore, the compressive load and an effective deformation was elucidated from the analytical consideration and experiment. The cross-section which is able to absorb greater crash energy was discussed by considering buckling mechanism, and it was verified by the experiment.

Engine knock is the one of the main issues to be addressed in developing high-efficiency spark-ignition (SI) engines. In order to improve the thermal efficiency of SI engines, it is necessary to develop effective means of suppressing knock. For that purpose, it is necessary to clarify the mechanism generating pressure waves in the end-gas region. This study examined the mechanism producing pressure waves in the end-gas autoignition process during SI engine knock by using an optically accessible engine. Occurrence of local autoignition and its development process to the generation of pressures waves were analyzed under several levels of knock intensity. The results made the following points clear. It was observed that end-gas autoignition seemingly progressed in a manner resembling propagation due to the temperature distribution that naturally formed in the combustion chamber. Stronger knock tended to occur as the apparent propagation speed of autoignition increased.

The use of a higher compression ratio is desirable for improving the thermal efficiency and specific power of spark-ignition engines, but it gives rise to a problem of engine knock. In the present research, an investigation was made of the role of the preflame reaction region of a spark-ignition engine in the occurrence of autoignition. Emission spectroscopy was used to measure the behavior of formaldehyde (HCHO) in a cool flame. In addition, measure the behavior of the faint light attributed to the HCO radical in a blue flame with the concurrent measurement of the OH radical. The emission waveforms measurements obtained for HCHO when n-heptane (ORON) was used as the fuel, It is thought that these tendencies correspond to the passage and degeneracy of a cool flame. Further, the emission waveforms measured for the HCO radical when blended fuels (6ORON, 8ORON) were correspond to that of a blue flame.

There are strong demands today to further improve the thermal efficiency of internal combustion engines against a backdrop of various environmental issues, including rising carbon dioxide (CO2) emissions and global warming. One factor that impedes efforts to improve the thermal efficiency of spark ignition engines is the occurrence of knocking. The aim of this study was to elucidate the details of knocking based on spectroscopic measurements and visualization of phenomena in the combustion chamber of a test engine that was operated on three primary reference fuels with different octane ratings (0 RON, 30 RON, and 50 RON). The ignition timing was retarded in the experiments to delay the progress of flame propagation, making it easier to capture the behavior of low-temperature oxidation reactions at the time knocking occurred.

This study investigated the effects of recirculated exhaust gas (EGR) and its principal components of N2, CO2 and H2O on moderating Homogeneous Charge Compression Ignition (HCCI) combustion. Experiments were conducted using two types of gaseous fuel blends of DME/propane and DME/methane as the test fuels. The addition rates of EGR, N2, CO2 and H2O were varied and the effects of each condition on HCCI combustion of propane and methane were investigated. The results revealed that the addition of CO2 and H2O had the effect of substantially delaying and moderating rapid combustion. The addition of N2 showed only a slight delaying and moderating effect. The addition of EGR had the effect of optimally delaying the combustion timing, while either maintaining or increasing the indicated mean effective pressure and indicated thermal efficiency ηi.

Homogeneous Charge Compression Ignition (HCCI) combustion has attracted considerable interest in recent years as a new combustion concept for internal combustion engines. On the other hand, two combustion concepts proposed for two-cycle spark-ignition (SI) engines are Active Thermo-Atmosphere Combustion (ATAC) and Activated Radical (AR) combustion. The authors undertook this study to examine the similarities and differences between HCCI combustion and ATAC (AR) combustion. Differences in the low-temperature oxidation reaction behavior between these two combustion processes were made clear using one test engine.

Effects of measurement method, coolant temperature and fuel composition on soot emissions were examined by engine experiments. By reducing the pressure fluctuation in the sampling line, the measured soot emissions with better stability and reproducibility could be obtained. With lower coolant temperatures, larger soot emissions were yielded at much advanced fuel injection timings. Compared to gasoline, soot emissions with a blend fuel of normal heptane, isooctane and toluene were significantly decreased, suggesting the amounts of aromatic components (toluene or others) should be increased to obtain a representative fuel for the predictive model of particulate matter in SIDI engines.

We have investigated into the torsional rigidity of spot-welded box section beam and reported on the torsional rigidities of double and single hat beams, the warping of which is restrained at both ends perfectly, using warping torsion theory of spot-welded box section beam we have proposed. In this paper, as a further analysis, we report on following three cases, 1) A case where the warping is restrained elastically at both ends. 2) A case where torsional moment varies longitudinally. 3) A case where pitch of spot-welds varies longitudinally.

Unresolved issues of Homogeneous Charge Compression Ignition (HCCI) combustion include an extremely rapid pressure rise on the high load side and resultant knocking. Studies conducted to date have examined ways of expanding the region of stable HCCI combustion on the high load side such as by applying supercharging or recirculating exhaust gas (EGR). However, the effect of applying EGR gas to supercharged HCCI combustion and the mechanisms involved are not fully understood. In this study, the effect of EGR gas components on HCCI combustion was investigated by conducting experiments in which external EGR gas was applied to supercharged HCCI combustion and also experiments in which nitrogen (N2) and carbon dioxide (CO2) were individually injected into the intake air pipe to simulate EGR gas components. In addition, HCCI combustion reactions were analyzed by conducting chemical kinetic simulations under the same conditions as those of the experiments.