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Low NOx and soot free premixed diesel combustion can be realized by increasing ignition delays in low oxygen atmospheres, as well as the combustion here also depends on fuel ignitability. In this report single intermittent spray combustion with primary reference fuels and a normal heptane-toluene blend fuel under several oxygen concentrations in a constant volume combustion vessel was analyzed with high-speed color video and pressure data. Temperature and KL factor distributions are displayed with a 2-D two-color method. The results show that premixing is promoted with a decrease in oxygen concentration, and the local high temperature regions, above 2200 K, as well as the duration of their appearance decreases with the oxygen concentration. With normal heptane, mild premixed diesel combustion can be realized at 15 vol% oxygen and there is little luminous flame.

Diesel-like combustion of an emulsified blend of water and diesel fuel in a constant volume chamber vessel was visualized with high speed color video, further analyzing with a 2-D two color method and shadowgraph images. When the temperature at the fuel injection is 900 K, here while the combustion with unblended diesel fuel in the vessel is similar to ordinary diesel combustion with diffusive combustion, combustion with the emulsified fuel is similar to premixed diesel combustion with a large premixed combustion and very little diffusive combustion. With the emulsified fuel the flame luminosity and temperature are lower, the luminous flame and high temperature regions are smaller, and the duration of the luminous flame is shorter than with diesel fuel. This is due to promotion of premixing with increases in the ignition delay and decreases in the combustion temperature with the water vaporization.

The volatile organic compounds (VOC) from diesel engines, including formaldehyde and benzene, are concerned and remain as unregulated harmful substances. The substances are positively correlated with THC emissions, but the VOC and aldehyde compounds at light load or idling conditions are more significant than THC. When coolant temperatures are low at light loads, there are notable increases in formaldehyde and acetaldehyde, and with lower coolant temperatures the increase in aldehydes is more significant than the increase in THC. When using ultra high EGR so that the intake oxygen content decreases below 10%, formaldehyde, acetaldehyde, benzene, and 1,3-butadiene increase significantly while smokeless and ultra low Nox combustion is possible.

To get accurate indicator diagrams without the use of pressure transducers, the strain and the displacement of the various parts of engine structures that would have some relationship with the pressure variation in the cylinder were measured and analyzed mathematically. By measuring the strain of the cylinder head bolts, the horizontal displacement of the crank shaft end, and the vertical displacement of the intake valve stem, we realized that the indicator diagrams could be obtained easily without a passage from the interior to the outside of the combustion chamber. Accurate indicator diagrams were estimated by applying the pressure-strain diagram obtained from the static pressure test in the cylinder to the strain variation in the cylinder head bolts. On this occasion, the accuracy of the estimated indicator diagrams could be improved by providing the cylinder head system with a one degree freedom vibration system.

Ultra low emissions and high performance combustion was achieved with a combination of high EGR, a three-way catalyst, and a highly oxygenated liquid fuel, neat dimethoxy methane (DMM), in an ordinary DI diesel engine. The smokeless nature of neat DMM effectively allowed stoichiometric diesel combustion by controlling BMEP with EGR. NOx, THC, and CO emissions were reduced with a three-way catalyst. At lower BMEP with excess air, the EGR effectively reduced NOx. High-speed video in a bottom view type engine revealed that luminous flame decreased with increased fuel oxygen content and almost disappeared with DMM.

Significant improvements in exhaust emissions and engine performance in an ordinary DI diesel engine were realized with highly oxygenated fuels. The smoke emissions decreased sharply and linearly with increases in oxygen content and entirely disappeared at an oxygen content of 38 wt-% even at stoichiometric conditions. The NOx, THC, and CO were almost all removed with a three-way catalyst under stoichiometric diesel combustion at both the higher and lower BMEP with the combination of EGR and a three-way catalyst. The engine output for the highly oxygenated fuels was significantly higher than that with the conventional diesel fuel due to the higher air utilization.

Diesel combustion and exhaust gas emissions under transient operation (when fuel amounts abruptly increased) were investigated under a wide range of operating conditions with a newly developed gas sampling system. The relation between gas emissions and piston wall temperatures was also investigated. The results indicated that after the start of acceleration NOx, THC and smoke showed transient behaviors before reaching the steady state condition. Of the three gases, THC was most affected by piston wall temperature; its concentration decreased as the wall temperature increased throughout the acceleration except immediately after the start of acceleration. The number of cycles, at which gas concentrations reach the steady-state value after the start of acceleration, were about 1.2 times the cycle constant of the piston wall temperature for THC, and 2.3 times for smoke.

Time resolved changes in unburned hydrocarbon emissions and their components were investigated in a DI diesel engine with a specially developed gas sampling system and gas chromatography. The tested transient operations include starting and increasing loads. At start-up with high equivalence ratios the total hydrocarbon (THC) at first increased, and after a maximum gradually decreased to reach a steady state value. Reducing the equivalence ratio of the high fueling at start-up and shortening the high fueling duration are effective to reduce THC emissions as long as sufficient startability is maintained. Lower hydrocarbons, mainly C1-C8, were the dominant components of the THC and mainly determined the THC behavior in the transient operations while the proportion of hydrocarbon (HC) components did not significantly change. The unregulated toxic substances, 1,3 butadiene and benzene were detected in small quantities.

Time series analysis of diesel exhaust gas emissions under transient operation was carried out using a uniquely developed gas sampling system to efficiently collect all exhaust gas throughout transient cycles. The effects of fuel properties and other engine operation parameters on the exhaust emissions under transient runs when fuel amounts abruptly increase were analyzed. The results showed that THC increased abruptly to 2 or 6 times the final steady-state concentration immediately after the start of acceleration and then decreased to the steady-state values after 70∼200 cycles. At acceleration, NOx increased abruptly to about 80 % of the final NOx concentration, and then increased gradually to reach the final values after 60∼500 cycles. The behaviors of THC and NOx during transient operation can be described by exponential functions of the elapsed cycle numbers and the final emission concentrations.

The authors have reported significant smoke reduction in twin shaped semi-premixed diesel combustion with a newly designed combustion chamber to distribute the first and the second sprays into upper and lower layers. However, the first stage premixed combustion tends to advance far from the TDC, resulting in lowering of thermal efficiencies. In this report, improvement of thermal efficiency by optimizing the combustion phase with lower ignitability fuels was identified with the divided combustion chamber. The experiment was conducted with four fuels with different cetane numbers. The first stage premixed combustion can be retarded to the optimum phase with the fuel with cetane number 38, establishing high efficiencies.

To improve the combustion characteristics in semi-premixed diesel combustion, consisting in the first-stage premixed combustion of the primary fuel injection and the second-stage spray combustion of the secondary injection, the effect of splitting the primary injection was investigated in a diesel engine and analyzed with a CFD. The indicated thermal efficiency improves due to reductions in heat transfer losses to the in-cylinder wall and the combustion noise is suppressed with the split primary injections. The CFD analysis showed that the reduction in heat transfer loss with the split primary injections is due to a decrease in the combustion quantity near the combustion chamber wall.

Semi-premixed diesel combustion with a twin peak shaped heat release with the two-stage fuel injection (twin combustion) has the potential to establish efficient, low emission, and low noise operation. However, with twin combustion at low loads the indicated thermal efficiencies are poorer than at medium loads due to the lower combustion efficiencies. In this report, to increase the combustion efficiencies at low loads, the thermal efficiency related parameters were investigated in a 0.55 L single cylinder diesel engine. The results show that the indicated thermal efficiency improves with increases in the intake gas temperatures at low loads. However, at the higher loads where the combustion efficiencies are somewhat higher the indicated thermal efficiencies decrease with increases in the intake gas temperatures due to increases in the cooling losses.

To evaluate the relation between the intake air temperature (Tair-in), low temperature heat release (LTHR) and high temperature heat release (HTHR), a supercharged 4-cylinder engine with intake air heating, high compression pistons and a pressure transducer in each cylinder was introduced Eleven pure hydrocarbon components were blended into 23 different model fuels, labeled BASE MC01-MC11, and K01-K11. BASE is a mixture of equal proportion of each of the 11 pure hydrocarbons. The difference between MC series and K series fuels is in the amount of pure hydrocarbon added to the BASE: 6.5vol% for MC series fuels and 17.5vol% for K series fuels. Engine tests were performed with BASE and MC01-MC11 fuels at Tair-in=50°C (IMEP 530kPa), 80°C (IMEP 420kPa), and 100°C (IMEP 380kPa).

Diesel soot suppression effects of catalytic fuel additives for a range of fuels with different properties were investigated with calcium naphthenate. A single cylinder DI diesel engine and a thermobalance were used to determine the soot reduction and its mechanism for seven kinds of fuels. Experimental results showed that the catalytic effect of the fuel additive was different for the different fuels, and could be described by a parameter considering cetane number and kinematic viscosity. The fuel additives reduced soot more effectively for fuels with higher cetane number and lower kinematic viscosity. This result was explained by soot oxidation characteristics for the different fuels. Oxidation of soot with the metallic additive proceeds in two stages: stage I, a very rapid oxidation stage; and stage II, a following slow or ordinary oxidation stage.

A study was performed in which the effects on the regulated emissions from a commercial small DI diesel engine were measured for different refinery-derived fuel blends. Seven different fuel blends were tested, of which two were deemed to merit more detailed evaluation. To investigate the effects of fuel properties on the combustion processes with these fuel blends, two-color pyrometry was used via optically accessible cylinderheads. Additional data were obtained with one of the fuel blends with a heavy-duty DI diesel engine. California diesel fuel was used as a baseline. The fuel blends were made by mixing the components typically found in gasoline, such as methyl tertiary-butyl ether (MTBE) and whole fluid catalytic cracking gasoline (WH-FCC). The mixing was performed on a volume basis. Cetane improver (CI) was added to maintain the same cetane number (CN) of the fuel blends as that of the baseline fuel.

The objective of the present research is to investigate the effects on diesel engine combustion and NOx and PM emission characteristics in case of blending the ordinary diesel fuel with biodiesel in passenger car diesel engines. Firstly, we conducted experiments to identify the combustion and emissions characteristics in a modern diesel engine complying with the EURO 4 emission standard. Then, we developed a numerical simulation model to explain and generalize biodiesel combustion phenomena in detail and generalize emission characteristics. The experimental and simulation results are useful to reduce biodiesel emissions by controlling engine operating and design parameters in the diesel engine. Engine tests were conducted and a mathematical model created to investigate the effects of 40% and 100% methyl oleate modeled fuel representing Jatropha-derived biodiesel on diesel combustion and emission characteristics, over a wide range of passenger car DI diesel engine operating conditions.

Fuel temperature in the injector of small direct injection gasoline engine is high. On some conditions it is higher than saturated temperature. Over saturated temperature spray characteristics greatly change. In order to predict in-cylinder phenomena accurately, it is important to understand spray behavior and mixture process above saturated temperature. Therefore spray shape, mixture formation process and Sauter mean radius were (SMR) measured in a constant volume chamber. And based on the measurement result initial spray boundary conditions were arranged so that spray characteristics over saturated temperature could be represented by using CFD code KIVA-3[1]. Moreover KIVA-3 code was combined with detailed chemical kinetics code Chemkin II to predict combustion products. [2] Calculated combustion process was validated with visualization of chemiluminescence. As a result, spray shape and penetration length have good agreement with measured ones for each fuel temperature.

This paper deals with the effects of flash-boiling injection of various kinds of fuels on spray characteristics, combustion, and engine performance in DI and IDI diesel engines. It is known that spray characteristics change dramatically at the boiling point of fuel. When the fuel temperature increases above the boiling point, the droplet size decreases apparently and the spray spreads much wider. At higher fuel temperatures, above the boiling point, the apparent effects are a lower smoke density and improved thermal efficiency at higher loads, resulting from the shorter combustion duration; it is thus possible to obtain a markedly improved engine performance in engines with a low air-utilization chamber. Remarkable changes in heat release with the increase in fuel temperature are; an increase in premised combustion quantity and shortening of the combustion duration. The changes in smoke emission and thermal efficiency for different engine types are also considered in this paper.

To improve urban air pollution, stringent emissions regulations for heavy-duty diesel engines have been proposed and will become effective in Japan, the EU, and the United States in a few years. To comply with such future regulations, it is critical to investigate the effects of intake and injection parameters and fuel properties on engine performance, efficiency and emissions characteristics, associated with the use of aftertreatment systems. An experimental study was carried out to identify such effects. In addition, the KIVA-3 code was used to gain insight into cylinder events. The results showed improvements in NOx-Smoke and BSFC trade-offs at high-pressure injection in conjunction with EGR and supercharging.

A supercharged 4-cylinder engine was introduced to evaluate how fuel properties affect engine combustion and performance in homogeneous charge compression ignition (HCCI) operation. In this study, choosing from 12 hydrocarbon constituents, model fuels were mixed to have the same distillation but different octane numbers (RON=70, 80, 92). For each fuel, RON distribution against distillation is same to keep the same octane number in cylinder vapor during the air-fuel compression process. To confirm the appropriateness of model fuels and test procedures, regular gasoline (RON=90) was also included. From the combustion analysis it was clear that the low temperature heat release depends on fuel characteristics. RON92 fuel has a small low temperature heat release, and a high temperature heat release combusts slowly.