Search Results

Hydrogen engines are required to provide high thermal efficiency and low nitrogen oxide (NOx) emissions. There are many possible combinations of injection pressure, injection timing, ignition timing, lambda and EGR rate that can be used in a direct-injection system for achieving such performance. In this study, several different combinations of injection and ignition timings were classified as possible combustion regimes, and experiments were conducted to make clear the differences in combustion conditions attributable to these timings. Lambda and the EGR rate were also evaluated for achieving the desired performance, and indicated thermal efficiency of over 45% was obtained at IMEP of 0.95 MPa. It was found that a hydrogen engine with a high-pressure direct-injection system has a high potential for improving thermal efficiency and reducing NOx emissions.

Hydrogen spark-ignition (SI) engines based on direct-injection (DI) promise significant advantages in terms of thermal efficiency and power output, as well as a means of overcoming problems related to knocking, backfiring, and pre-ignition. In a DI hydrogen engine, the fuel/air mixture is formed by injecting a jet of hydrogen into the air inside the combustion chamber. An Ar-ion laser beam was used as a light source to visualize the hydrogen jet in a constant-volume chamber. This allowed us to study the structure of the jet in addition to other physical processes resulting from hydrogen gas injection. Combustion experiments were conducted in a single-cylinder SI optical research engine equipped with a DI system to detect the early kernel growth assisted by the spark, as well as flame propagation. Various equivalence ratios and fuel injection timings were analyzed to identify the effects on combustion.

Homogeneous charge compression ignition (HCCI), has the potential to improve the fuel economy and to reduce NOx emission significantly. Spark plug in SI engine and fuel injector in diesel engine can be used directly to control the start of combustion and the combustion period. However, the combustion of HCCI engine is controlled by the chemical kinetic mainly due to the temperature histories in the cylinder. Therefore the combustion process of HCCI engine cannot be directly controlled. Ion sensors such as a spark plug or a gasket are useful to detect the combustion information in production engines. In this study, the ion current was measured in an HCCI engine with the heated charge mixture of fuel and air without EGR when the charge temperature, equivalence ratio and fuel were varied. Simultaneously in-cylinder pressure was measured and the rate of heat release was calculated. The relationship between the rate of heat release and the ion current is mainly discussed.

This paper describes simultaneous attainment in improving fuel consumption, output power and reducing HC emissions with a direct injection S.I. engine newly developed in Nissan. Straight intake port is adopted to increase discharge coefficient under WOT operation and horizontal swirl flow is generated by a swirl control valve to provide stable stratified charge combustion under part load conditions. As a result, fuel consumption is reduced by more than 20% and power output is improved by approximately 10%. Moreover, unburned HC is reduced by equivalently 30% in engine cold start condition. An application of diagnostic and numerical simulation tools to investigate and optimize various factors are also introduced.

Non-intrusive measurement of transient unburned gas temperatures was developed with a fiber-optic heterodyne interferometry system. Using the value of the Gladstone-Dale constant for DME gas and combustion pressure we can calculate the in-cylinder temperature inside unburned and burned region. In this experimental study, it was performed to set up a fiber-optic heterodyne interferometry technique to measure the temperature before and behind the combustion region in a DME-HCCI engine. At first, measured temperature was almost the same as the temperature history assuming that the process that changes of the unburned and the burned are polytropic. In addition, we measured the temperature after combustion which of condition was burned gas with DME-HCCI combustion. The developed heterodyne interferometry used the spark-plug-in fiber-optic sensor has a good feasibility to measure the unburned and burned temperature history.

Emissions remain a critical issue affecting engine design and operation, while energy conservation is becoming increasingly important. One approach to favorably address these issues is to achieve homogeneous charge combustion and stratified charge combustion at lower peak temperatures with a variable compression ratio, a variable intake temperature and a trapped rate of the EGR using NVO (negative valve overlap). This experiment was attempted to investigate the origins of these lower temperature auto-ignition phenomena with SCCI and CAI using gasoline fuel. In case of SCCI, the combustion and emission characteristics of gasoline-fueled stratified-charge compression ignition (SCCI) engine according to intake temperature and compression ratio was examined. We investigated the effects of relative air/fuel ratio, residual EGR rate and injection timing on the CAI combustion area.

Investigation of knocking combustion in a hydrogen spark-ignition engine is one of the major challenges for future vehicle development. The knock phenomenon in a Spark-Ignition (SI) engine is caused by autoignition of the unburned gas ahead of the flame. The explosive combustion of the end-gas creates a pressure wave that leads to damage of the cylinder wall and the piston head of the engine. We observed autoignition in the end-gas region due to compression by the propagating flame front using a high-speed colour video camera through the optically accessible cylindrical quartz window on the top of the cylinder head. Moreover, a high-speed monochrome video camera operating at a speed of 250, 000 frame/s was used to measure the pressure wave propagation. The goal of this research was to improve our ability to describe the effect of the autoignition process on the end-gas and propagating pressure wave during knocking combustion with the help of a high-speed video camera.

The combustion and exhaust emissions characteristics of a supercharged dual-fuel natural gas engine with a single cylinder were analyzed. We focused on EGR (Exhaust Gas Recirculation) to achieve higher thermal efficiency and lower exhaust emissions. The combustion of diesel fuel (gas oil) as ignition sources was visualized using a high-speed video camera from the bottom of a quartz piston. The luminous intensity and flame decreased as the EGR rate increased. Furthermore, the ignition delay became longer due to the EGR. Characteristics of the combustion and exhaust emissions were investigated with changing EGR rates under supercharged conditions. The indicated mean effective pressure and thermal efficiency decreased with increasing EGR rate. In addition, NOx emissions decreased due to the EGR. In this study two-stage combustion was observed.

This study investigated the effect of some pilot fuel injection parameters, like injection timing, injection pressure and injection quantity on engine performance and exhaust emissions of a supercharged producer gas-diesel dual fuel engine. The engine has been tested to be used as a co-generation engine and its power output is an important matter. Experiments have been done to optimize the injection timing, injection pressure and injection quantity for the maximization of engine power. At constant injection pressures, there is an optimum amount of pilot injection quantity for that maximum engine power is developed without knocking and within the limit of maximum cylinder pressure. Above or below of that amount engine power is decreased. Higher injection pressures generally show better results than lower ones. However, good results can also be obtained with lower injection pressure, if maximum power timings can be selected.

The results of our previous study showed that applying hydrogen (H2) to homogeneous charge compression ignition (HCCI) combustion with the assist of di-methyl ether (DME) as a supplement improved thermal efficiency compared with homogeneous hydrogen-fueled spark ignition (SI) combustion [1, 2]. As a general characteristic of HCCI combustion, however, stable engine operation is limited to a narrow region by the occurrence of misfiring and abrupt combustion like knocking. The onset of heat release is still not sufficiently controllable to achieve optimum engine performance. The objective of this study is to control the onset of the main heat release of hydrogen-fueled HCCI combustion by adopting spark ignition to assist autoignition. The results showed that improved thermal efficiency and reduced combustion fluctuation were achieved by attaining MBT operation with the support of spark ignition.

In this study, fuel concentration measurements in a spark-ignition (SI) engine with ethanol blended gasoline were carried out using an optical sensor installed in the spark plug with laser infrared absorption technique. The spark plug sensor for in-situ fuel concentration measurement was applied to a port injected SI engine. The molar absorption coefficients of ethanol blended gasoline were determined for various pressures and temperatures in advance using a constant volume vessel with electric heating system. Ethanol blended gasoline with high volumetric ratios shows lower molar absorption coefficients due to lower molar absorption coefficients of ethanol. The molar absorption coefficients of ethanol blended gasoline can be estimated by considering the molar fraction of each component.

Hydrogen engines are required to provide high thermal efficiency and low nitrogen oxide (NOX) emissions. There are many possible combinations of injection timing, ignition timing, lambda and EGR rate that can be used in a direct-injection system for achieving such performance. In this study, NOX emissions of natural aspirated 4 cylinders engine with management strategies involving the injection timing, ignition timing, lambda and the EGR rate were evaluated under a Japanese JE05 emissions test cycle. Finally, the paper projects the potential of direct injection hydrogen engine for obtaining high output power and attaining low NOX emissions of 0.7 g/kWh under the emission test cycle.

The results of this study make clear the characteristics of electrode performance deterioration in terms of cell voltage reduction in polymer electrolyte fuel cells (PEFCs) caused by the presence of certain quantities of carbon monoxide and/or hydrogen sulfide in the anode feed. AC impedance measurements of the anode and cathode potentials revealed that both electrode potentials showed deterioration in the presence of each type of poisoning gas. This suggests that the poisoning gases permeated the electrolyte membrane and transferred to the cathode, causing performance deterioration by poisoning the catalyst. In addition, AC impedance measurements indicated that the presence of hydrogen sulfide in the anode feed increased the membrane impedance, thus implying some poisoning effect even on the electrolyte membrane.

It is well known that the wavelet transform is a useful time-frequency analysis method for an unsteady signal and major attention has been focused on the selection of the mother wavelet (MW) because the MW plays an important role in the wavelet transform. In this study, we analyze the pressure signal in a spark-ignition engine and the vibration of the engine block measured by a knock sensor under the knocking conditions when knocking is caused. We then propose a new method of the knocking detection that utilizes the knocking signal measured with a knock sensor as a MW. We call this method the Instantaneous Correlation Method (ICM). The degree of similarity between the MW and the vibration of the engine block was judged and only the knocking signal from the vibration of the engine block was extracted. The results obtained here show that the method proposed in this study is useful for knocking detection even if the engine speed is very high of 6000rpm.

Hydrogen is expected to be one of the most prominent fuels in the near future for solving greenhouse problem, protecting environment and saving petroleum. In this study, a dual fuel engine of hydrogen and diesel oil was investigated. Hydrogen was inducted in a intake port with air and diesel oil was injected into the cylinder. The injection timing was changed over extremely wide range. When the injection timing of diesel fuel into the cylinder is advanced, the diesel oil is well mixed with hydrogen-air mixture and the initial combustion becomes mild. NOx emissions decrease because of lean premixed combustion without the region of high temperature of burned gas. When hydrogen is mixed with inlet air, emissions of HC, CO and CO2 decrease without exhausting smoke while brake thermal efficiency is slightly smaller than that in ordinary diesel combustion.

It is important to develop the technique for measuring the cycle-to-cycle variation of combustion in order to reduce the fuel consumption of the commercial spark ignition engine. In previous study, we had proposed using the spark plug as an ion probe to measure the appearance time of maximum pressure under the lean mixture conditions of the research engine. In this paper the combustion diagnostics for the commercial engine was performed using the spark plug as an ion probe. Under idling conditions the ion current often appeared during the exhaust process. This ion current is dominated by the flame contact area and the flame velocity. In this case there is good correlation between the characteristic value of the ion current and the indicated mean effective pressure (IMEP). Finally using the spark plug as an ion probe can detect the combustion quality under conditions with large cyclic variation.

A dual fuel engine fueled with methane from an inlet port and ignited with diesel fuel was prepared. This study focuses on the effects of early injection and exhaust gas recirculation (EGR) on the characteristics of combustion and exhaust emissions. The injection timing was changed between TDC and 50 degrees before the TDC. In the early injection timing, smoke was never seen and hydrocarbons were smaller compared with those at the normal injection timing. However, the combustion becomes too early to obtain an appropriate torque when the equivalence ratio increases. Then, moderate EGR was very effective to force the combustion to retard with lower NOx, higher thermal efficiency and almost the same hydrocarbons and carbon monoxide. The engine operated even under the condition of stoichiometric mixture.

Homogeneous Charge Compression Ignition (HCCI) combustion with dimethyl ether has been carried out in a single cylinder engine with a transparent piston. The engine was operated at 800 rpm with a wide-open throttle. The intake-premixed mixture was preheated with an electric heater to promote auto-ignition. HCCI combustion with dimethyl ether indicates multi-stage heat releases. Investigations were conducted with visualization of combustion in the cylinder and detailed and temporal spectroscopic measurements using spectrometer. In order to understand reaction mechanism of auto-ignition and combustion mechanism in HCCI engine, spectrum analysis of chemiluminescence was carried out.

A new ignition-combustion concept named PCC (Plume Ignition Combustion Concept), which ignite rich mixture plume in the middle of injection period or right after injection of hydrogen is completed, is proposed by the authors in order to reduce NOx emissions in high engine load conditions with minimizing trade-offs on thermal efficiency. In this study fundamental requirements of hydrogen jet to optimize PCC are investigated by using single and multi-hole nozzle with a combination of high speed laser shadowgraphy to visualize propagating flame. As a result, it was infered that igniting the mixture plume in the middle of injection period with minimizing jet penetration to chamber wall is effective reducing NOx formation even further.

Effects of injection parameters on combustion and emission characteristics of diesel PCCI engine operating on optical and test engine was investigated. PCCI combustion was achieved through slightly narrow included angle injector, low compression ratio coupled with exhaust gas recirculation. Analysis based on diesel spray evolution, combustion process visualization and analysis was carried out. Spray penetration was evaluated and related to the exhaust emissions. Advancing the injection timing and EGR extended the ignition delay, decreased NOx emissions and increased HC, smoke and CO emissions. Higher injection pressure led to low emissions of NOx, smoke, HC and comparable CO. Optimum spray targeting position for minimum emission was identified. Impingement on the piston surface led to deterioration of emissions and increased fuel consumption while spray targeting the upper edge of Derby hat wall showed improvement in emission and engine performance.