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Premixed diesel combustion blending high volatility fuels into diesel fuel were investigated in a modern diesel engine. First, various fractions of normal heptane and diesel fuel were examined to determine the influence of the blending of a highly ignitable and volatile fuel into diesel fuel. The indicated thermal efficiency improves almost linearly with increasing normal heptane fraction, particularly at advanced injection timings when the fuel is not injected directly into the piston cavity. This improvement is mainly due to decreases in the other losses, ϕother which are calculated with the following equation based on the energy balance. ηu: The combustion efficiency calculated from the exhaust gas compositions ηi: The indicated thermal efficiency ϕex: The exhaust loss calculated from the enthalpy difference between intake and exhaust gas The decreases in the other losses with normal heptane blends are due to a reduction in the unburned fuel which does not reach the gas analyzer.

A homogeneous-charge compression-ignition (HCCI) engine system that was fuelled with dimethyl ether (DME) and methanol-reformed gas (MRG) has been proposed in the previous research. Adjusting the proportion of DME and MRG can effectively control the ignition timing of the engine. In the system, both fuels are to be produced from methanol in onboard reformers utilizing the engine exhaust gas heat. While hydrogen contained in MRG has the main role of the ignition control, hydrogen increases with carbon dioxide in the methanol reforming. This paper investigates the influence of carbon dioxide on HCCI combustion engine with the ignition control by hydrogen. Both thermal and chemical effects of carbon dioxide are analyzed.

To extend the operational range of premixed diesel combustion, fuel reformation by piston induced compression of rich homogeneous air-fuel mixtures was conducted in this study. Reformed gas compositions and chemical processes were first simulated with the chemistry dynamics simulation, CHEMKIN Pro, by changing the intake oxygen content, intake air temperature, and compression ratio. A single cylinder diesel engine was utilized to verify the simulation results. With the simulation and experiments, the characteristics of the reformed gas with respect to the reformer cylinder operating condition were obtained. Further, the thermal decomposition and partial oxidation reaction mechanisms of the fuel in extremely low oxygen concentrations were obtained with the characteristics of the gas production at the various reaction temperatures.

Port injection of ethanol addition as an ignition inhibitor was implemented to control ignition timing and expand the operating range in DME fueled HCCI combustion. The ethanol reduced the rate of low-temperature oxidation and consequently delayed the onset of the high-temperature reaction with ultra-low NOx over a wide operating range. Along with the ethanol addition, changes in intake temperature, overall equivalence ratio, and engine speed are investigated and shown to be effective in HCCI combustion control and to enable an extension of operation range. A chemical reaction analysis was performed to elucidate details of the ignition inhibition on low-temperature oxidation of DME-HCCI combustion.

Palm oil has the important advantage of productivity compared to other vegetable oils such as rapeseed oil and soybean oil. However, the cold flow performance of palm oil methyl ester (PME) is poorer than other vegetable oil based biodiesel fuels. Previous research by the authors has shown that ethanol blending into PME improves the cold flow performance and considerably reduces smoke emission. The reduced smoke may be expected to allow an expansion in the EGR limit and lead to reduced NOx. This paper experimentally analyses the influence of EGR on smoke and NOx emissions from the diesel combustion with PME/ethanol blended fuel. The mechanisms in the smoke reduction are also analyzed.

Premixed diesel combustion modes including low temperature combustion and MK combustion are expected to realize smokeless and low NOx emissions. As ignition must be delayed until after the end of fuel injection to establish these combustion modes, methods for active ignition control are being actively pursued. It is reported that alcohols including methanol and ethanol strongly inhibit low temperature oxidation in HCCI combustion offering the possibility to control ignition with alcohol induction. In this research improvement of diesel combustion and emissions by ethanol intake port injection for the promotion of premixing of the in-cylinder injected diesel fuel, and by increased EGR for the reduction of combustion temperature.

The thermal cracking and polyaromatic hydrocarbon (PAH) formation processes of dimethyl ether (DME), ethanol, and ethane were investigated with chemical kinetics to determine the soot formation mechanism of oxygenated fuels. The modeling analyzed three processes, an isothermal constant pressure condition, a temperature rising condition under a constant pressure, and an unsteady condition approximating diesel combustion. With the same mole number of oxygen atoms, the DME rich mixtures form much carbon monoxide and methane and very little non-methane HC and PAH, in comparison with ethanol or ethane mixtures. This suggests that the existence of the C-C bond promotes the formation of PAH and soot.

Reformed fuel from hydrocarbons or alcohol mainly consists of hydrogen, carbon monoxide and carbon dioxide. The composition of the reformed fuel can be varied to some extent with a combination of a thermal decomposition reaction and a water gas shift reaction. Methanol is known to decompose at a relatively low temperature. An application of the methanol reforming system to an internal combustion engine enables an exhaust heat recovery to increase the heating value of the reformed fuel. This research analyzed characteristics of combustion, exhaust emissions and cooling loss in an internal combustion engine fueled with several composition of model gases for methanol reformed fuels which consist of hydrogen, carbon monoxide and carbon dioxide. Experiments were made with both a bottom view type optical access single cylinder research engine and a constant volume combustion chamber.

Methanol has many advantages as a fuel for fuel cells compared with hydrogen. The direct methanol type system consists of simple and compact equipment, and suited for automobile use. This research analyzed characteristics of power output and thermal efficiency in a direct methanol fuel cell. The measuring system for low concentration methanol in a water solution using the non-dispersive infrared (NDIR) was developed. Influences of electrolyte membrane thickness, cell temperature, and methanol solution concentration on power output and thermal efficiency were analyze.

Adjusting the proportion of two fuels with different ignition properties is an effective technique for controlling ignition timing in homogeneous charge compression ignition (HCCI) combustion. One of the authors has proposed an HCCI combustion engine system fueled with dimethyl ether (DME) with a high cetane number and methanol reformed gas (MRG) with a high anti-knock property in the previous research. Both DME and MRG are to be produced from methanol by onboard reformers utilizing the exhaust heat from the engine in the system. The research has shown that adjusting the proportion of DME and MRG effectively controlled the ignition timing and load in HCCI combustion of the two fuels. High overall thermal efficiency has been shown over a wide operable range. While the MRG used in the research was the thermally decomposed methanol, which consists of hydrogen and carbon monoxide, methanol can be reformed into various compositions of hydrogen, carbon monoxide and carbon dioxide.

This study analyzes the factors influencing the thermal efficiency of a homogeneous charge spark-injection (SI) engine fuelled with hydrogen, focusing on the degree of constant volume and cooling loss. The cooling loss from the burning gas to the cylinder walls is quantitatively evaluated by analyzing the cylinder pressure diagram and exhaust gas composition. The degree of constant volume burning and constant volume cooling are also obtained by fitting the Wiebe function to the rate of heat release calculated using the cylinder pressure diagram. A comparison of combustion and cooling characteristics of hydrogen and methane combustion reveals that cooling loss in hydrogen combustion is higher than that of methane combustion due to the short quenching distance and rapid burning velocity during hydrogen combustion. It is also suggested that the high cooling loss observed during hydrogen combustion reduces thermal efficiency.

Smokeless and ultra low NOx combustion without knocking in a dual-fuel diesel engine with induced LPG as the main fuel was established with a uniquely developed piston cavity divided by a lip in the sidewall. A small quantity of diesel fuel was directly injected at early compression stroke into the lower part of the cavity as an ignition source for this confined area, and this suppressed explosively rapid combustion just after ignition and spark-knock like combustion at later stage. A combination of the divided cavity, EGR, and intake air throttling was effective to simultaneously eliminate knocking, and reduce THC and NOx significantly.

Homogeneous charge compression ignition (HCCI) combustion enables higher thermal efficiency and lower NOx emission to be achieved in internal combustion engines when compared with conventional combustion systems. Control of proportion of high cetane number and low cetane number fuels is an effective technique for controlling ignition timing and load in HCCI combustion. The aim of this paper is to analyze the characteristics of the HCCI combustion of hydrogen, carbon monoxide and dimethyl ether (DME) in a single cylinder engine. A mixture of hydrogen and carbon monoxide with a composition of 67% hydrogen and 33% carbon monoxide called methanol-reformed gas (MRG) was used as the low cetane number fuel and DME as the high cetane number fuel. Both MRG and DME can be reformed from methanol in endothermic reactions. The endothermic reactions make waste heat recovery in fuel reforming possible by using the heat from the exhaust gases.

Direct injection of various ignition suppressors, including water, methanol, ethanol, 1-propanol, hydrogen, and methane, was implemented to control ignition timing and expand the operating range in an HCCI engine with induced DME as the main fuel. Ultra-low NOx and smoke-less combustion was realized over a wide operating range. The reaction suppressors reduced the rate of low-temperature oxidation and consequently delayed the onset of high-temperature oxidation. Analysis of the chemical kinetics showed a reduction of OH radical in the premixed charge with the suppressors. Among the ignition suppressors, alcohols had a greater impact on OH radical reduction resulting in stronger ignition suppression. Although water injection caused a greater lowering of the temperature, which also suppressed ignition, the strong chemical effect of radical reduction with methanol injection resulted in the larger impact on suppression of oxidation reaction rates.

Light naphtha, which exhibits two-stage ignition, was induced from the intake manifold for ignition enhancement and a low ignitability fuel or water, which does not exhibit low temperature oxidation, was directly injected early in the compression stroke for ignition suppression in an HCCI engine. Their quantitative balance was flexibly controlled to optimize ignition timing according to operating condition. Ultra-low NOx and smokeless combustion without knocking or misfiring was realized over a wide operating range. Alcohols inhibit low temperature oxidation more strongly than other oxygenated or unoxygenated hydrocarbons, water, and hydrogen. Chemical kinetic modeling for methanol showed a reduction of OH radical concentration before the onset of low temperature oxidation, and this may be the main mechanism by which alcohols inhibit low temperature oxidation.

The engine performance and the exhaust gas emissions in a dual fuel compression ignition engine with natural gas as the main fuel and a small quantity of pilot injection of diesel fuel with the ultra-high injection pressure of 250 MPa as an ignition source were investigated at 0.3 MPa and 0.8 MPa IMEP. With increasing injection pressure the unburned loss decreases and the thermal efficiency improves at both IMEP conditions. At the 0.3 MPa IMEP the THC and CO emissions are significantly reduced when maintaining the equivalence ratio of natural gas with decreasing the volumetric efficiency by intake gas throttling, but the NOx emissions increase and excessive intake gas throttling results in a decrease in the indicated thermal efficiency. Under the 250 MPa pilot injection condition simultaneous reductions in the NOx, THC, and CO emissions can be established with maintaining the equivalence ratio of natural gas by intake gas throttling.

The HCCI engine offers the potential of low NOx emissions combined with diesel engine like high efficiency, however HCCI operation is restricted to low engine speeds and torques constrained by narrow noise (HCCI knocking) and misfiring limits. Gasoline like fuel vaporizes and mixes with air, but the mixture may auto-ignite at the same time, leading to heavy HCCI knocking. Retarding the CA50 (the crank angle of the 50% burn) is well known as a method to slow the maximum pressure rise rate and reduce HCCI knocking. The CA50 can be controlled by the fuel composition, for example, di-methyl ether (DME), which is easily synthesized from natural gas, has strong low temperature heat release (LTHR) characteristics and ethanol generates strong LTHR inhibitor effects. The utilization of DME-ethanol binary blended fuels has the potential to broaden the HCCI engine load-speed range.

Silent, clean, and efficient combustion was realized with emulsified blends of aqueous ethanol and diesel fuel in a DI diesel with pilot injection and cooled EGR. The pilot injection sufficiently suppressed the rapid combustion to acceptable levels. The thermal efficiency with the emulsified fuel improved as the heat release with the pilot injection was retarded to near top dead center, due to poor ignitability and also due to a reduction in afterburning. With the emulsified fuel containing 40 vol% ethanol and 10 vol% water (E40W10), the smokeless operation range can be considerably extended even under low fuel injection pressure or low intake oxygen content conditions.

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.

Cycle-to-cycle changes in diesel exhaust gas emissions were investigated under two transient operation patterns: One, “an interval step decreasing and increasing load”, where the fuel amount is rapidly decreased from high to low loads, and after an interval, Δtint the fuel amount is abruptly returned to the initial level. The other is “a ramp increasing load”, where the fuel amount is increased gradually. Except just after the step increase in fuel amounts, the THC emissions were almost completely determined by the piston wall temperature and fuel amount. However, the THC concentrations immediately after the step increase in fuel amounts were much higher than the value of the corresponding steady state operation with the same piston wall temperature. This overshoot concentration, ΔTHC, was almost constant at different intervals, Δtint and it can be suppressed by ramp increased loading.