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In this paper, spray characteristics were examined to deduce the effect of ambient gas properties. Considered ambient properties were the viscosity μa and density ρa, and thus the kinematic viscosity νa. The objective of this paper is to reveal the effect of compressibility of the ambient gas to spray formation. In the experiments, the changed ranges were And a standard-sac volume nozzle of hole diameter dn =0.25 mm (ln/dn=3.0) was used at constant injection pressure difference (Δp=16.2 MPa). Also the injection pressure was varied in the range of 55 to 120 MPa with a mini-sac volume nozzle of hole diameter dn =0.20 mm (ln/dn =5.5). Several different gases were used to change the ambient viscosity at a room temperature. From the experiments, it is obtained that larger the viscosity, the more the spray spreads in the radial direction, thus the spray angle gets larger and the tip penetration became shorter.

The use of biodiesel fuels as an alternative fuel for petroleum diesel fuel is very effective for the reduction of CO2 emission, because biodiesel is produced from renewable biomass resources. Biodiesel is usually blended to conventional diesel fuel in various proportions. It is possible that this biodiesel blending causes the problems on emission characteristics of modern diesel engine, because it could be confirmed that the application of neat biodiesel to modern diesel engines whose control parameters were optimized for conventional diesel fuel deteriorated the emission performances. It is necessary to clarify the effect of biodiesel blending on exhaust emissions of modern diesel engine. Rapeseed oil methyl ester (RME) was selected as a biodiesel used in this study.

The use of biomass fuels for vehicles has been a focus of attention all over the world in terms of prevention of global warming, effective utilization of resources and local revitalization. For the purpose of beneficial use of unused biomass resources, the movement of the use of bioethanol and biodiesel made from them has spread in Japan. In Japan, biodiesel is mainly made from waste cooking oil collected by local communities or governments, and in terms of local production for local consumption, it is used as neat fuel (100% biofuel) or mixed with diesel fuel in high concentration for the vehicles. On the other hand, extremely low emission level must be kept for not only gasoline vehicles but also diesel vehicles in the post new long-term regulation implemented from 2009 in Japan.

Research on alternative fuels is necessary to reduce CO2 emissions. Hydrotreated Vegetable Oil (HVO) of light fuel physically improves spray and combustion characteristics. Fatty Acid Methyl Ester (FAME) is an oxygenated fuel and its combustion characteristics are chemically improved, although its spray characteristics such as penetration and atomization are deteriorated. The purpose of this study is to understand the effects of blending HVO, which has carbon neutral (CN) characteristics, with FAME, which also has CN characteristics, on spray and combustion characteristics, and to further improve emission such as THC and Smoke. This report presents the effect of the combination of improved spray characteristics and oxygenated fuel on emissions. Spray characteristics such as penetration, spray angle and spray volume were investigated by shadowgraph photography.

The effect of boiling point difference as well as the flash boiling of two-component normal paraffin fuels on combustion and exhaust emission has been examined under different test conditions. To obtain a wide variation in boiling point between components different high boiling point fuels (n-undecane, n-tridecane and n-hexadecane) were blended with a low boiling point fuel (n-pentane) and different low boiling point fuels (n-pentane, n-hexane, and n-heptane) were blended with a high boiling point fuel (n-hexadecane). In addition the volume fraction of n-pentane was varied to have the best mixture ratio with n-tridecane. These fuel combinations exhibit different potential for flash boiling based on a certain ambient condition. The results indicate that though the potential for flash boiling is the highest for a mixture of n-pentane and n-hexadecane it emits about 20% higher PM than a mixture of n-pentane and n-tridecane.

LES of non-evaporative diesel spray have been performed to investigate the effects of breakup models of Modified TAB, WAVE and KHRT model on computational results. KIVALES that is LES version of KIVA code was used for base code. In our KIVALES, CIP scheme was incorporated in order to suppress the numerical diffusion. Results showed that the breakup model is significantly affected on the calculated spray shape, because the droplet diameter determined by breakup models affects on the transmittance of the droplet momentum into the ambient gas, the evolution of the vortex structure in the gas phase and the droplet dispersion by the vortex structure.

In this study, a numerical experiment using a 2D convective equation and LES of an evaporative diesel spray for different convective schemes has been performed to examine effects of convective schemes on a fuel-air mixture formation of the diesel spray simulation and to determine the convective scheme used in KIVALES. In addition to KIVALES original schemes, such as QSOU, PDC and IDC, CIP was incorporated into KIVALES in order to calculate the convective terms with low numerical diffusion. The numerical experiment using the 2D convective equation showed that the numerical diffusion of CIP scheme was lowest in the convective schemes used in present study. However CIP scheme used was not a monotone scheme completely due to the overshoot and the undershoot of the scalar provided near the boundary. Hence, CIP scheme was employed for only the convective term of the LES momentum equation, while the other convective schemes were calculated using QSOU, which is a monotone scheme.

In recent years, internal combustion engine using hydrogen gas, has attracted attention as one solution to the problem of global warming. Hydrogen gas has excellent combustion characteristics such as wide limits of inflammability and fast burning velocity because of high diffusion rate. Therefore, it has been made to obtain stable ignition and combustion by adding hydrogen with lean mixture in spark ignition engines using hydrocarbon fuels and to be attempted efficient operation by engine researchers. The purpose of this study is to reduce cooling loss in a gas engine using hydrogen gas and hydrogen Mixer system (Mixer) engine was remodeled to hydrogen Port Injection (PI) system engine. In this report, the heterogeneity of hydrogen mixture is clarified by comparing the combustion characteristics of the Mixer and the PI, and the effect of the difference in hydrogen supply systems on cooling loss is system. Ignition delay of the PI system is shorter than that of the Mixer.

The purpose of this study is to reduce cooling loss in gas engines using hydrogen. In this report, the effect of different hydrogen-CNG supply methods on combustion and exhaust characteristics of SI engine were investigated. As a result, the 13A-port-injection caused sharp heat release at hydrogen addition ratio (RH) of 20 %, with a maximum brake thermal efficiency of 27.5 %. Also, the hydrogen-port-injection promotes combustion above RH=40 % and reduces cooling loss, resulting in a maximum brake thermal efficiency of 31.0 % at RH=80 %, 1.8 pt higher than that of the 13A-port-injection.

Application of biodiesel fuel (BDF) to diesel engine is very effective to reduce CO2 emission, because bio-diesel is carbon neutral in principle. However, when biodiesel was applied to conventional diesel engines without modification for biodiesel, NOx emission was increased by the change in fuel characteristics. It is necessary to introduce some strategies into diesel engines fuelled with biodiesel for lower NOx emission than conventional diesel fuel case. The purpose of this study is to reveal that exhaust gas recirculation (EGR) is one of the solutions for the reduction of NOx emission and meeting the future emission regulations when using biodiesel. Neat Rapeseed oil methyl ester (RME) as a biodiesel (B100) was applied to diesel engines equipped with high pressure loop (HPL) EGR system and low pressure loop (LPL) EGR system. Cooled HPL EGR was increased during steady-state operations and JE05 transient mode tests.

The use of biofuel is essential for the reduction of greenhouse gas emission. This paper highlights the use of biodiesel as a means of reducing greenhouse gas emission from the diesel engine of heavy-duty vehicles. Biodiesel is fatty acid methyl ester (FAME) obtained through ester exchange reaction by adding methanol to oil, such as rapeseed oil, soybean oil, palm oil, etc. The CO₂ emission from combustion of biodiesel is defined to be equivalent to the CO₂ volume absorbed by its raw materials or plants in their course of growth. On the other hand, however, biodiesel is known to increase the NOx emission when compared with operating with conventional diesel fuel, then suppressing this increase is regarded as a critical issue. This study is intended to identify the fuel properties of biodiesel free from increase in the NOx emission.

Fuel design concept has been proposed for low emission and combustion control in engine systems. In this concept, the multicomponent fuels, which are mixed with a high volatility fuel (gasoline or gaseous fuel components) and a low volatility fuel (gas oil or fuel oil components), are used for artificial control of fuel properties. In addition, these multicomponent fuels can easily lead to flash boiling which promote atomization and vaporization in the spray process. In order to understand atomization and vaporization process of multicomponent fuels in detail, the model for flash boiling spray of multicomponent fuel have been constructed and implemented into KIVA3V rel.2. This model considers the detailed physical properties and evaporation process of multicomponent fuel and the bubble nucleation, growth and disruption in a nozzle orifice and injected fuel droplets.

The spray structure under the pressurized atmosphere at a room temperature was examined by the various photographic methods. The fuel flow inside the nozzle was investigated by the transparent model nozzles. The experimental analysis of sprays yielded the spray dispersing angle, the distribution of fuel droplets inside the spray and the jet intact core length. The obtained results of those spray characteristics showed that the spray structure is divided into two spatial regimes due to their formation mechanisms. Within 10 mm from the nozzle, the spray dispersion is dominated by the turbulent states of fuel which are initiated inside the nozzle. At distance from the nozzle z > 20 - 40 mm, the spray consists of an induced gas vortex street whose length is about half of the spray width. It is proposed that the kinematic viscosity of ambient gas is a important factor which rules the process of momentum exchange form the fuel jet to the ambient gas.

A single cylinder engine has been run with direct-injection premixed charge compression ignition (PCCI) operation. The operation is fueled with primary reference fuels for a wide variety of injection timing and equivalence ratio to investigate the effect of charge stratification and octane rating on PCCI combustion. The test results showed that although the change of the injection timing can gain the high combustion efficiency for a wide range of equivalence ratio, the combustion phasing where the high combustion efficiency is accomplished is not varied only by changing the injection timings. Therefore, the only change of injection timings does not improve the thermal efficiency which is influenced by the combustion phasing. On the other hand, at the fixed compression ratio, inlet air temperature and so on, the octane rating is useful in altering the combustion phasing.

This work presents the ignition delay time characteristics of oxygenated fuel sprays under simulated diesel engine conditions. A constant volume combustion vessel is used for the experiments. The fuels used in the experiments were three oxygenated fuels: diethylene glycol dibutyl ether, diethylene glycol diethyl ether, and diethylene glycol dimethyl ether. JIS 2nd class gas oil was used as the reference fuel. The ambient gas temperature and oxygen concentration were ranging from 700 to 1100K and from 21 to 9%, respectively. The results show that the ignition delay of each oxygenated fuel tested in this experiments exhibits shorter than that of gas oil fuel for the wide range of ambient gas conditions. Also, NTC (negative temperature coefficient) behavior which appears under shock tube experiment for homogenous fuel-air mixture was observed on low ambient gas oxygen concentration for each fuel. And at the condition, the ignition behavior exhibits two-stage phase.

Considering the bell-shaped temperature dependence of soot particle formation, the control of flame temperature has a possibility to drastically suppress of soot formation. Furthermore, oxygenated fuels are very effective on soot reduction, and the use of these kinds of fuels has a potentiality for smokeless diesel combustion. In this paper, the effects of flame lift-off and flame temperature on soot formation in oxygenated fuel sprays were experimentally investigated using a constant volume combustion vessel which simulated diesel engine conditions. The diffusion flame lift-off length was measured in order to estimate the amount of the oxygen entrained upstream of the flame lift-off length in the fuel jet. This was determined from time-averaged OH chemiluminescence imaging technique. Also, the flame temperature and soot concentration were simultaneously evaluated by means of two-color method.

Homogeneous Charge Compression Ignition (HCCI) is effective for the simultaneous reduction of soot and NOx emissions from diesel engine. In general, high octane number and volatility fuels (gasoline components or gaseous fuels) are used for HCCI operation, because very lean mixture must be formed during ignition delay of the fuel. However, it is necessary to improve fuel injection systems, when these fuels are used in diesel engine. The purpose of the present study is the achievement of HCCI combustion in DI diesel engine without the large-scale improvements of engine components. Various high octane number fuels are mixed with diesel fuel as a base fuel, and the mixed fuels are directly applied to DI diesel engine. At first, the cylinder pressure and heat release rate of each mixed fuel are analyzed. The ignition delay of HCCI operation decreases with an increase in the operation load, although that of conventional diesel operation does not almost varied.

A dual fuel operation with different reactivity fuels has the possibility of optimizing performance and emissions in premixed charge compression ignition engines by controlling the spatial concentration and distribution of both fuels. In the present study, n-heptane and i-octane were independently injected through two different injectors. In-cylinder pressure analysis and emissions measurement were performed in a compression ignition engine. Injection timings, fuel quantity ratio between the injections were changed for the two cases, in which one fuel was injected using a port fuel injection system while the other was directly injected into the cylinder, in order to drastically vary mixture distributions and ignition timings. In addition, an optical diagnostic was performed in a rapid compression and expansion machine to develop an understanding of the ignition processes of the two mixtures.

We have proposed the application of Exhaust Gas Recirculation (EGR) gas dissolved fuel which might improve spray atomization through effervescent atomization instead of high injection pressure. Since EGR gas is included in the spray of EGR gas dissolved fuel, it directly contributes to combustion, and the further reduction of NOx emissions is expected rather than the conventional external EGR. In our research, since highly contained in the exhaust gas and highly soluble in the fuel, CO2 was selected as the dissolved gas to simulate EGR gas dissolved. In this paper, the purpose is to evaluate the influence of the application of CO2 gas dissolved fuel on the combustion characteristics and emission characteristics inside the single cylinder, direct injection diesel engine. As a result, by use of the fuel, smoke was reduced by about 50 to 70%, but NOx reduction does not have enough effect.

Urea SCR (Selective Catalytic Reduction) system has high potential of reducing NOx. But such as system durability and safety under deteriorated catalysts conditions have not been well enough clarified because it is new technology for vehicles. In this paper, current NOx emission level of an engine equipped with urea SCR system is discussed and then exhaust emission characteristics were analyzed when the SCR catalyst and/or oxidation catalyst lose their functions. When both SCR and oxidation catalyst were de-activated, not only NOx but also PM increased remarkably, which were much more than the engine-out emissions. Oxidation catalyst downstream of SCR catalyst was effective to suppress such deteriorations.