Search Results

This study aims to investigate the combustion and flow phenomena in a stoichiometrically operated methane-fueled passive pre-chamber ignited gas engine. The combustion phenomena are visualized with a high-speed camera and the chemical properties are resolved by Large Eddy Simulation (LES) turbulent model with the SAGE combustion approach. Results reveal that a highly compressed unburnt gas of intermediate fuel species emerges from the pre-chamber before the flame ejection due to the high-pressure difference which promptly consumes the main chamber charge and accelerates combustion. Moreover, the nozzle diameter and spark plug orientation significantly affect the flame propagation as well as the overall engine performance.

To control the auto ignition in end-gas region and to achieve higher thermal efficiency in a natural gas dual fuel engine operated under PREMIER combustion mode where the end-gas auto ignition occurs without knocking-like oscillation, the EGR (exhaust gas recirculation) and supercharging were applied. The EGR rate and the intake air pressure as well as the pilot injection timing of diesel fuel were varied, and the profiles of the in-cylinder pressure, the exhaust emissions and the heat balance were examined at the indicated mean effective pressure around 680 kPa. The experimental results showed that higher thermal efficiency can be achieved with the combination of the PREMIER combustion and the EGR rate of 30% due to the improvements in the combustion efficiency and the degree of constant volume heat release while reducing the cooling loss.

In this research, a spark plug with an optical fiber has been developed to obtain the emission spectra from the spark discharge and flame kernel. This developed spark plug with an optical fiber can obtain the time series of emission spectra from the spark discharge and Initial flame kernel in the real spark-ignition engine using EMCCD spectrometer. The plasma vibrational temperature of the spark discharge can be measured using the emission spectra from the electrically excited CN violet band system. The plasma of the spark discharge and gas rotational temperature of the initial flame kernel can be also measured using emission spectra from OH* radicals (P and R branches). The plasma temperature of the spark discharge was almost 8,000 K and the gas temperature of the Initial flame kernel approached that of the adiabatic flame temperature.

The authors have previously proposed a plume ignition and combustion concept (i.e., PCC combustion), in which a hydrogen fuel is directly injected to the combustion chamber in the latter half of compression stroke and forms a richer mixture plume. By combusting the plume, both cooling losses and NOx formation are reduced. In this study, thermal efficiency was substantially improved and NOx formation was reduced with PCC combustion by optimizing such characteristics as direction and diameter of the jets in combination with combustion of lean mixture. Output power declined due to the lean mixture, however, was recovered by supercharging while keeping NOx emissions at the same level. Thermal efficiency was further improved by slightly re-optimizing the jet conditions.

The present study helps to understand the local combustion characteristics of PREmixed Mixture Ignition in the End-gas Region (PREMIER) combustion mode while using increasing amount of natural gas as a diesel substitute in conventional CI engine. In order to reduce NOx emission and diesel fuel consumption micro-pilot diesel injection in premixed natural gas-air mixture is a promising technique. New strategy has been employed to simulate dual fuel combustion which uses well established combustion models. Main focus of the simulation is at detection of an end gas ignition, and creating an unified modeling approach for dual fuel combustion. In this study G-equation flame propagation model is used with detailed chemistry in order to detect end-gas ignition in overall low temperature combustion. This combustion simulation model is validated using comparison with experimental data for dual fuel engine.

The objective of this study is to investigate the initial flame propagation characteristics of turbulent flame in an engine cylinder through time-series analysis of radical emissions. A spark plug with optical fiber was developed in this study. The plug sensor is M12 type that makes it possible to mount in practical engine. The spark plug sensor can detect radical emissions in time-resolved spectra through time-series spectroscopic measurement. In this spectra, some kinds of radical emissions such as OH*(306nm), CH*(431nm) and C2*(517nm) based on principle of chemiluminescence are observed. In this study, the spark plug sensor was applied to both compression-expansion machine (CEM) and practical engine. As a result of CEM with bottom viewed high-speed camera, three kinds of spectra could be detected.

Bio-gas as an internal combustion (I.C.) engine fuel has many advantages such as cheaper fuel cost, low emission levels and especially the neutral recirculation loop of carbon dioxide, which is one of the principal factors in global warming. In this study, positive potentialities of bio-gas were investigated using a micro co-generation engine. The mixing ratio of methane (CH4) and carbon dioxide (CO2) was changed to simulate various types of bio-gases. Intake air and fuel flow rates were controlled to change the equivalence ratio. The engine load condition could be changed with the electric output power used. Base on the result, the higher CO2 content rate slowed down the engine speed in the same load condition and the combustion speed generally decreased under the same load condition with maintaining the engine speed. However thermal efficiency increased with lean burn conditions and NOX emission decreased with higher CO2 mixing rates.

A single cylinder, supercharged dual fuel gas engine with micro-pilot fuel injection is operated using methane only and methane-hydrogen mixtures. Methane only experiments were performed at various equivalence ratios and equivalence ratio of 0.56 is decided as the optimum operating condition based on engine performance, exhaust emissions and operation stability. Methane-hydrogen experiments were performed at equivalence ratio of 0.56 and 2.6 kJ/cycle energy supply rate. Results show that indicated mean effective pressure is maintained regardless of hydrogen content of the gaseous fuel while thermal efficiency is improved and presence of hydrogen reduces cyclic variations. Increasing the fraction of hydrogen in the fuel mixture replaces hydrocarbon fuels and reduces carbon monoxide and hydrocarbon emissions.

Hydrogen spark-ignition (SI) engines based on direct-injection (DI) have been investigated because of their potential for high thermal efficiency and solving the problems related to knocking, backfiring, and pre-ignition. Wide range flammability limits in hydrogen engine enable smooth engine operation for a very lean mixture with low NOX. However, a too lean mixture may increase ignition delay and causes severe cyclic variations. There is a possibility that the turbulence occurred during injection of fuel surround the spark plug in the combustion chamber is major contributor to this phenomenon. To overcome this problem, a better understanding of the spark discharge and spark ignition during transient hydrogen jet is necessary. Therefore, it is very important to study an effect of local equivalence ratio and behavior of spark discharge in SI engine. This paper describes a mixing process of hydrogen jet using spark-induced breakdown spectroscopy (SIBS) in a constant volume vessel.

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.

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.

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.

This paper describes the development and application of a spark plug sensor using an infrared absorption technique to quantify the instantaneous residual gas concentration near the spark plug. The residual gas fraction inside engine cylinder is assumed to be proportional to CO2 concentration. The relationship between CO2 concentration and absorption strength of CO2 was determined for various pressures and temperatures in advance using a constant volume vessel with electric heating system. The spark plug sensor for in-situ CO2 concentration measurement was applied to a compression-expansion engine and also to a port injected motorcycle SI engine. It was possible to qualify the CO2 concentration inside residual gas during the compression stroke using the developed optical system with new spark plug sensor in compression-expansion machine.

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.

In this study, residual gas fraction measurements in a spark-ignition engine were carried out using an optical sensor installed in the spark plug with infrared absorption method. The residual gas fraction inside engine cylinder is proportional to the CO2 concentration. Infrared absorption method was applied and an infrared lamp and optical filter (center wavelength: around 4.3 μm) that coincides with the absorption lines of CO2 was used as a light source.The molar absorption coefficient of CO2 is discussed and compared to results in the HITRAN database. The effect of water vapor absorption doesn't affect the absorption of CO2. The absorption characteristics of CO2 were determined in advance using a constant volume vessel. Molar absorption coefficient depends on the CO2 concentration and ambient pressure and temperature, and wavelength of absorption line.

This paper describes the development and application of a spark plug sensor using a 3.392 μm infrared absorption technique to quantify the instantaneous gasoline concentration near the spark plug. We developed an in situ laser infrared absorption method using a spark plug sensor and a 3.392 μm He-Ne laser as the light source; this wavelength coincides with the absorption line of hydrocarbons. First, we established a database of the molar absorption coefficients of premium gasoline at different pressures and temperatures, and determined that the coefficient decreased with increasing pressure above atmospheric pressure. We then demonstrated a procedure for measuring the gasoline concentration accurately using the infrared absorption technique. The history of the molar absorption coefficient of premium gasoline during the experiment was obtained from the established database using measured in-cylinder pressures and temperatures estimated by taking the residual gas into consideration.

A small Cassegrain optics sensor was developed to measure local chemiluminescence spectra and the local chemiluminescence intensities of OH*, CH*, and C2* in a four-stroke spark-ignition (SI) engine in order to investigate the propagation characteristics of the turbulent premixed flame. The small Cassegrain optics sensor was an M5 type that could be installed in place of a pressure transducer. The measurements could be used to estimate the flame propagation speed, burning zone thickness, and local air/fuel (A/F) ratio for each cycle. The specifications of the small Cassegrain optics sensor were the same as those used for previous engine measurements. In this paper, measurements were made of several A/F ratios using gasoline to fuel the model engine. The performances of two Cassegrain optics sensors were compared to demonstrate the advantages of the new small sensor by measuring the local chemiluminescence intensities of a turbulent premixed flame in the model engine.

A heterodyne interferometry system with a fiber-optic sensor was developed to measure the temperature history of unburned gas in a spark-ignition engine. A polarization-preserving fiber and metal mirror were used as the fiber-optic sensor to deliver the test beam to and from the measurement region. This fiber-optic sensor can be assembled in an engine cylinder head without a lot of improvements of an actual engine. Adjustment system in the sensor was revised to face the distributed index lens with metal mirror. Before the flame arrived at the developed fiber-optic sensor, measured temperature was almost same with the temperature history after the spark, assuming that the process that changes the unburned gas is adiabatic. In situ unburned gas temperature measurements before knocking in a commercially produced SI engine can be carried out using developed fiber-optic heterodyne interferometry system.

Experimental investigations of fuel breakup very close to nozzle of practical high-pressure swirl injector, which is used in gasoline direct injection (GDI) engine, were carried out. In GDI engines, fuel is directly injected into cylinder therefore the spray characteristics and mixture formation are of primary importance. In this research, visualizations of primary spray formation process were demonstrated using a high-speed video camera (maximum speed: 1Mfps) with a long-distance microscope. Initial state and development of the spray were discussed under the different injection pressure condition. During the injection period, the length and thickness of the liquid sheet, which is produced from the nozzle exit, were measured using Ar-ion laser sheet and high-speed camera. Primary spray structure and behavior of liquid sheet, especially surface wave of liquid sheet, at nozzle exit were discussed using obtained images.