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Combustion is known to be affected by variations in the air-fuel mixture concentration, residual gas concentration, turbulent kinetic energy, ignition, etc. However, because each of these factors is related to cycle-to-cycle variations, their effects on combustion variation are unclear. The purpose of this study was to clarify the influences of the air-fuel mixture distribution near the spark plug and variation in the relative position of the ignition on the combustion variation. A 4-cylinder port injection gasoline engine was used as the test engine, and the combustion variation was investigated by measuring the cylinder pressure and air-fuel ratio (A/F) near the spark plug for each cycle using a micro-Cassegrain sensor for each cylinder. The air-fuel mixture distribution was calculated using a Reynolds averaged Navier-Stokes simulation, and the spatial region of the high ignition probability was determined from the gas flow velocity.

Dimethyl Ether (DME) is one of the major candidates for the alternative fuel for compression ignition (CI) engines. However, DME spray combustion characteristics are not well understood. There is no spray model validated against spray experiments at high-temperature and high-pressure relevant to combustion chambers of engines. DME has a lower viscosity and lower volumetric modulus of elasticity. It is difficult to increase injection pressure. The injection pressure remains low at 60 MPa even in the latest DME engine. To improve engine performance and reduce emissions from DME engines, establishing the DME spray model applicable to numerical engine simulation is required. In this study, high-speed observation of DME sprays at injection pressures up to 120 MPa with a latest common rail DME injection system was conducted in a constant volume combustion vessel, under ambient temperature and pressure of 6 MPa-920 K.

Exhaust gas recirculation (EGR) is widely used in diesel engines to reduce nitrogen oxide (NOx) emissions. However, a lacquer is formed on the EGR valve or EGR cooler due to particulate matter and other components present in diesel exhaust, causing serious problems. In this study, the mechanism of lacquer deposition is investigated using attenuated total reflection Fourier transform infrared spectrometry (ATR-FTIR) and scanning electron microscopy (SEM). Deposition of temperature-dependent lacquers was evaluated by varying the temperature of a diamond prism between 80 and 120 °C in an ATR-FTIR spectrometer integrated into a custom-built sample line, which branched off from the exhaust pipe of a diesel engine. Lacquers were deposited on the diamond prism at 100 °C or less, while no lacquer was deposited at 120 °C. Time-dependent ATR-FTIR spectra were obtained for approximately 2 h from the beginning of the experiment.

Diesel engines have better fuel economy over comparable gasoline engines and are useful for the reduction of CO2 emissions. However, to meet stringent emission standards, the technology for reducing NOx and particulate matter (PM) in diesel engine exhaust needs to be improved. A conventional selective catalytic reduction (SCR) system consists of a diesel oxidation catalyst (DOC), diesel particulate filter (DPF), and urea-SCR catalyst. Recently, more stringent regulations have led to the development of SCR systems with a larger volume and increased the cost of such systems. In order to solve these problems, an SCR catalyst-coated DPF (SCR/DPF) is proposed. An SCR/DPF system has lower volume and cost compared to the conventional SCR system. The SCR/DPF catalyst has two functions: combustion of PM and reduction of NOx emissions.

DME has lower energy content per unit volume than that of light oil (typical petroleum based diesel fuel). Roughly 1.8 times the quantity of DME is required to obtain equivalent content of light oil. DME also exhibits higher compressibility and much lower viscosity than light oil, so high pressure injection is not easy. Currently, DME engines have utilized a larger injection volume by enlarging the nozzle diameter with a relatively low injection pressure up to 60MPa. In order to obtain higher performance in future DME engines, high pressure fuel injection is considered essential, however the high pressure DME spray characteristics have not yet been understood. In this research, DME spray characteristics of high injection pressure up to 140MPa were examined using a constant volume vessel under engine-like temperature/pressure conditions.

For better understanding of the combustion characteristics in a direct injection dimethyl ether (DME) engine, the chemiluminescences of a burner flame and in-cylinder flame were analyzed using the spectroscopic method. The emission intensities of chemiluminescences were measured by a photomultiplier after passing through a monochrome-spectrometer. For the burner flame, line spectra were found nearby the wave length of 310 nm, 430 nm and 515 nm, arising from OH, CH and C2 radicals, respectively. For the in-cylinder flame, a strong continuous spectrum was found from 340 nm wave length to 550 nm. Line spectra were also detected nearby 310 nm, 395 nm and 430 nm, arising from OH, HCHO, and C2 radicals, respectively, partially overlapping with the continuous spectrum. Of these line spectra, 310 nm of OH radical did not overlapped with the continuous spectrum.

To date, the DME combustion mechanism has been investigated by in-cylinder gas sampling, numerical calculations and observation of combustion radicals. It has been possible to quantify the emission intensities of in-cylinder combustion using a monochromator, and to observe the emitting species as images by using band-pass filters. However, the complete band images were not observed since the broadband (thermal) intensity may be stronger than band spectra intensities. Emission intensities of DME combustion radicals from a pre-mixed burner flame have been measured using a spectroscope and photomultiplier. Results were compared to other fuels, such as n-butane and methane, then, in this study, to better understand the combustion characteristics of DME, emission intensities near CH bands of an actual DI diesel engine fueled with DME were measured, and band spectra emitted from the engine were defined. Near TDC, emission intensities did not vary with wavelength.

One of the key technologies in improving engine performance is flexible valve timing. New combustion systems such as Homogeneous Charge Compression Ignition (HCCI) can be realized by flexible valve operation. Usually the valve timing is determined only by engine crank angle and is not flexible. To overcome this problem, an electromagnetic actuator had been proposed. However, a conventional solenoid actuator always requires current and the efficiency is low. In this study, a new type of linear actuator that uses bias flux produced by a permanent magnet (PM) to reduce power consumption was proposed. First, a cylindrical actuator was developed. To achieve further power consumption reduction, miniaturization and high-speed drive, a seesaw type actuator was designed. An experimental setup was designed to confirm its characteristics. The results showed improved performance and a high possibility for practical use.

For better understanding of the in-cylinder combustion characteristics of DME, combustion radicals of a direct injection DME-Fueled compression ignition engine were observed using a spectroscopic method. In this initial report, the emission intensity of OH, CH, CHO, C2 and NO radicals was measured using a photomultiplier. These radicals could be measured with wavelength resolution (half-width) as about 3.3 nm. OH and CHO radicals appeared first, and then CH radical emission was detected. After that, the combustion radicals were observed using a high-speed image intensified video camera with band-pass filter. All of radicals were able to observe as images with half-width as 6 or about 10 nm. Rich DME leaked from nozzle was burning at the end of combustion. Therefore, the second light emission of C2 radical after the main combustion was observed.

Recently, dimethyl ether (DME) has been attracting much attention as a clean alternative fuel, since the thermal efficiency of DME powered diesel engine is comparable to diesel fuel operation and soot free combustion can be achieved. In this experiment, the effect of ambient pressure on DME spray was investigated with observation of droplet size such as Sauter mean diameter (SMD) by the shadowgraph and image processing method. The higher ambient pressure obstructs the growth of DME spray, therefore faster breakup was occurred, and liquid column was thicker with increasing the ambient pressure. Then engine performances and exhaust emissions characteristics of DME diesel engine were investigated with various compression ratios. The minimum compression ratio for the easy start and stable operation was obtained at compression ratio of about 12.

Dimethyl Ether (DME) is one of the major candidates for the next generation fuel for compression ignition (CI) engines. It has good self-ignitability and would not produce particulate, even at rich conditions. DME has proved to be able to apply to ordinary diesel engines with minimal modifications, but its combustion characteristics are not completely understood. In this study, the behavior of a DME spray and combustion process of a direct injection CI engine fueled with DME was investigated by combustion observation and in-cylinder gas sampling. To distinguish evaporated and non-evaporated zones of a spray, direct and schlieren imaging were carried out. The sampled gas from a DME spray was analyzed by gas chromatography, and the major intermediate product histories during ignition period were analyzed.

In this study, the main properties of two types of gas-to-liquid (GTL) fuels were investigated. Then, performance and emission characteristics of a compression ignition engine fueled with GTLs were investigated by comparison with diesel fuel. GTL1 was composed of 100% paraffin by volume, and GTL2 was composed of 99.8% paraffin and 0.2% aromatics by volume. Most GTL fuel properties were comparable to those of diesel fuel, while both fuels have a higher cetane number and lower sulphur. A diesel engine could be operated with GTL fueling without any special engine modifications. Our tests showed that with the high cetane number of GTLs, the ignition delay was shorter, and combustion started earlier than with diesel fuel. With GTL1 operation, THC and soot emissions were lower than with diesel fuel operation, and even lower with GTL2 fueling.

For better understanding of the in-cylinder combustion characteristics of DME, combustion radicals of a direct injection DME-Fueled compression ignition engine were observed using a spectroscopic method. In this initial report, the emission intensity of OH, CH, CHO, C2 and NO radicals was measured using a photomultiplier. These radicals could be measured with wavelength resolution (half-width) of about 3.3 nm. OH and CHO radicals appeared first, and then CH radical emission was detected. After that, the combustion radicals were observed using a high-speed image intensified video camera. C2 and CH radicals were able to observe roughly as images. However, the emission intensity of DME combustion was not strong enough to take OH, CHO and NO radical images. CH radical combustion occurred near the chamber wall and burned like a ring, as combustion progress, indicating active heat release occurred near the chamber wall.

Homogeneous charge compression ignition (HCCI) combustion of methane was performed using dimethyl ether (DME) as an ignition improver. The ignition mechanisms of the methane/DME/air HCCI process were investigated on the basis of the chemical kinetics. The engine test was also conducted to verify the calculation results, and to determine the operation range. Analysis of the results showed that DME was an excellent ignition improver for methane, having two functions of temperature rise and OH radical supply. It was also shown that the operation range was extended to an overall equivalence ratio of 0.54 without knocking, by controlling DME quantity.

In this study, a homogeneous mixture of natural-gas and air was used in a compression ignition engine to reduce NOx emissions and improve thermal efficiency. In order to control ignition timing and combustion, a small amount of DME was mixed with the natural-gas. Engine performance and the exhaust characteristics were investigated experimentally. Results show the following: the engine can run over quite a large load range if a certain amount of DME is added into natural-gas. By optimizing the proportion of DME to natural-gas, NOx emissions can be lowered to near zero levels if the mixture is lean enough. Thermal efficiency is higher than that obtained with normal diesel fuel operation.

A feasibility study of an LPG DI diesel engine has been carried out to study the effectiveness of two selected cetane enhancing additives: Di-tertiary-butyl peroxide (DTBP) and 2-Ethylhexyl nitrate (EHN). When more than either 5 wt% DTBP or 3.5 wt% 2EHN was added to the base fuel (100 % butane), stable engine operation over a wide range of engine loads was possible (BMEPs of 0.03 to 0.60 MPa). The thermal efficiency of LPG fueled operation was found to be comparable to diesel fuel operation at DTBP levels over 5 wt%. Exhaust emissions measurements showed that NOx and smoke levels can be significantly reduced using the LPG+DTBP fuel blend compared to a light diesel fuel at the same experimental conditions. Correlations were derived for the measured ignition delay, BMEP, and either DTBP concentration or cetane number. When propane was added to a butane base fuel, the ignition delay became longer.

In this study, the NO emission characteristics of a dimethyl ether fueled compression ignition (CI) engine were studied, and a suitable combustion control concept was developed. A three-zone thermo-chemical model was used to understand the basic NO formation characteristics with dimethyl ether. The experimental study was carried out using a small direct-injection diesel engine. Comparison of the experimental and calculated results showed that the dimethyl ether / air mixing process was relatively slow compared with diesel fuel, which is the main reason for the relatively high NO emissions with dimethyl ether operation, in spite of its lower adiabatic flame temperature. To reduce the high temperature period, turbulence was introduced into the combustion chamber by a high-turbulence combustion system, which reduced NO emissions. It became clear that acceleration of the mixing process is an important factor for NO reduction with dimethyl ether spray combustion.

To meet the strict emission regulations for diesel engines, an advanced processing device such as a Urea-SCR (selective catalytic reduction) system is used to reduce NOx emissions. The Real Driving Emissions (RDE) test, which is implemented in the European Union, will expand the range of conditions under which the engine has to operate [1], which will lead to the construction of a Urea-SCR system capable of reducing NOx emissions at lower and higher temperature conditions, and at higher space velocity conditions than existing systems. Simulations are useful in improving the performance of the urea-SCR system. However, it is necessary to construct a reliable NOx reduction model to use for system design, which covers the expanded engine operation conditions. In the urea-SCR system, the mechanism of ammonia (NH3) formation from injected aqueous urea solution is not clear. Thus, it is important to clarify this mechanism to improve the NOx reduction model.

Recently, highly sensitive near-IR laser absorption spectrometers have been employed to measure ammonia (NH3) emissions. These instruments allow in-situ measurements of highly time-resolved NH3 emission levels in automobile exhaust. However, the effect of the automobile exhaust CO2 in NH3 measurements has not been studied in detail. Because the CO2 concentration in automobile exhaust is 2 to 3 orders of magnitude higher than the NH3 concentration, there is a possibility that spectral overlap by CO2 lines and/or the spectral broadening of NH3 by CO2 could affect the measured NH3 levels. This study had two major objectives. First, the effect of CO2 on the measured NH3 concentration was assessed using our developed near-IR laser absorption spectrometer. The second objective was to provide on-board NH3 measurements in the hybrid gasoline automobile exhaust using the developed spectrometer. As a result, the CO2 in automobile exhaust was found to affect the measured NH3 concentration.

DiMethyl Ether (DME) has been known to be an outstanding fuel for combustion in diesel cycle engines for nearly twenty years. DME has a vapour pressure of approximately 0.5MPa at ambient temperature (293K), thus it requires pressurized fuel systems to keep it in liquid state which are similar to those for Liquefied Petroleum Gas (mixtures of propane and butane). The high vapour pressure of DME permits the possibility to optimize the fuel injection characteristic of direct injection diesel engines in order to achieve a fast evaporation and mixing with the charged gas in the combustion chamber, even at moderate fuel injection pressures. To understand the interrelation between the fuel flow inside the nozzle spray holes tests were carried out using 2D optically accessed nozzles coupled with modelling approaches for the fuel flow, cavitation, evaporation and the gas dynamics of 2-phase (liquid and gas) flows.