The expanding energy demand, surging oil prices, depleting oil reserves, environmental pollution and climate change problems associated with the utilization of fossil fuels have revived interest to ...find out clean alternative fuels. Methanol is one of the most competitive alternative fuels due to its liquid nature, high oxygen contents, and high octane number and could produce from renewable sources. In this review, recent engine experimental and computational studies concerned with methanol fumigation on diesel engine were summarized. Technical and safety issue such as physical and chemical effect, environmental and health risk associated with the use of this technology were discussed. Modeling and simulation, engine performance and emissions, and recent advanced concept for methanol fumigated diesel engine were then reviewed respectively. At the beginning, the chemical and physical effect by the addition of methanol on the diesel fuels combustion were analyzed. The results showed that the fumigation of methanol could significantly prohibit the formation of PAHs. Then, for engine experiments, the effect of methanol fumigation on performance, combustion and emission characteristics of DMDF diesel engines were analyzed. It is examined that the fumigation of methanol fuel could reduce diesel engine emissions without adverse impacts on the performance of diesel engines. Further, new engine concepts such as RCCI operated with methanol fumigated diesel engine has also been summarized. Finally, this article puts forward some suggestions for the researches of diesel methanol dual fuel engine in the future.
Diesel engine performance and emissions are closely related to fuel atomization and spray processes, which in turn are strongly influenced by nozzle geometry. In this study, five kinds of single-hole ...cylindrical injectors which have different orifice diameters (0.13–0.23mm) and lengths (0.7–1.0mm) were employed to research the effects of the nozzle geometry on spray droplet size distribution and corresponding combustion characteristics. The spray droplet size spatial distribution was measured with the Phase Doppler Particle Analyzer (PDPA). The results show that the Sauter Mean Diameter (SMD) reduces with the increase of the distance from injector tip and the SMD of the central axis is bigger than that of the periphery. With the increase of the injection pressure (40–120MPa), the spray SMD decreases significantly. In addition, as the orifice diameter goes smaller, the SMD decreases and the effect of the orifice diameter on the spray SMD becomes weak. Meanwhile, as the orifice length goes longer, the SMD decreases when the orifice diameter is 0.13mm. And then, the combustion characteristics were experimentally investigated in a constant volume chamber with optical access. Time-resolved images of the natural luminosities (indicator of soot) from the combustion process were captured by high speed camera and combustion pressure was also acquired. It is found that there is a good corresponding relationship between spray SMD, combustion heat release rate and flame luminosity. That is to say, the way to decrease SMD reduces greatly the natural luminosities and improves combustion heat release rate. This article presents the effects of nozzle geometry on droplet size distribution and combustion, and provides important references for injector manufacture.
•PM and dry-soot from turbo-charged diesel engine with DMDF were measured.•Relation on dry-soot emission and PM was analyzed.•Effects of DMDF, DOC and intake air temperature on PM and dry-soot were ...investigated.•Particle number and mass concentration on different loads with DMDF were realized.
The effects of diesel/methanol dual fuel (DMDF) combustion, diesel oxidation catalyst (DOC) and intake air temperature on dry-soot and PM (particulate matter) emissions were investigated. Experiments were conducted on a 6-cylinder turbo-charged, inter-cooling HD (heavy duty) diesel engine modified to diesel/methanol dual fuel combustion mode. The pressurized methanol was induced into the intake manifold with six injectors and mixed with boost fresh air to form homogeneous mixtures and then ignited by pilot diesel in the cylinder. The amount of injected methanol was varied in accordance with engine power output while the amount of diesel fuel was remained constant under different operation conditions. Experimental results show that at low and medium loads, there is a significant decrease in the dry-soot emission in DMDF mode before the DOC, but a little increase at high load. An important phenomenon was observed that the mass and number concentrations of particulate matter significantly decrease at low and medium loads, due to the increase in fuel burned in the premixed mode and a reduction in diesel fuel involved, while they increase when the tested engine operates on the high engine condition, due to the spontaneous combustion of methanol and a reduction in oxygen for diesel in cylinder. After the DOC, the particulate mass and number concentrations are significantly reduced at all engine loads. Moreover, the temperature of intake air decreases with the increase of methanol injection, and the particulate number and mass concentrations in DMDF mode decrease with the decrease of the intake air temperature.
► The inhibit effect of methanol on the ignition of diesel (n-heptane) is analysed. ► A skeletal model for the combustion process of pure fuel and blends is created. ► The model includes 38 reactions ...and 30 species. ► The model has been validated by experiment and detailed mechanism.
It has been found in previous experimental studies that the ignition of diesel or n-heptane is delayed by methanol addition. However, detailed analysis of the interaction between the two fuels especially under low temperature oxidation has not been reported previously. In order to discover the chemical mechanism and create a skeletal model which can be coupled with 3-D simulation software efficiently, following works were conducted: Firstly, by using a detailed n-heptane oxidation mechanism which was slightly revised, the reaction paths analysis was conducted to seek the coupled relationship between n-heptane and methanol; Secondly, based on the reaction paths and sensitive analysis, a skeletal kinetic model including only 38 reactions related to 30 kinds of species was created to predict the ignition delay and the combustion of methanol/n-heptane blends as well as each pure fuel. The detailed mechanism analysis results show that when two fuels are blended, the radical pool is the only bridge between them. OH· is converted into H2O2 when affected by methanol, and H2O2 then frozen due to its high decomposition activation energy in the temperature below about 1000K, thus the reaction activity of the whole system deceases; The skeletal model test result shows that the ignition delay of the n-heptane, methanol and the blends is well predicted under various equivalence ratios, initial temperatures and pressures compared with the results of experiments or detailed mechanism. HCCI engine test also show that the ignition, in-cylinder temperature as well as the major species all have satisfactory predictions.
Diesel/natural gas dual fuel (DNDF) and diesel/methanol dual fuel (DMDF) both have very good potential for use in alternative energy technologies for internal combustion engine. In this work, a ...comparative study was done to better understand the ignition characteristics of dual fuel combustion. First, their apparent ignition characteristics were studied experimentally on a constant volume chamber and apparent ignition delay correlations of DNDF and DMDF were built; second, chemical kinetic analysis was used to explain the phenomenon observed; lastly, an improved KIVA-3 V code was applied to study the importance of the chemical interaction between diesel and methane or methanol on diesel ignition timing in an engine. Experimental results showed that both methanol and methane addition retarded the ignition of diesel and methane retarded less, which was due to the dehydrogenation of methanol and methane, reaction CH3 + HO2 = CH3O + OH and the formation of H2O2. CFD numerical results showed that, in the DMDF engine, the chemical interaction by methanol addition was the most important factor for the retarding of diesel ignition timing compared to other factors, such as the reduction of the amount of diesel, lower oxygen concentration, and the higher specific heat in the intake charge; in the DNDF engine, the effects of the chemical interaction and the reduction of the amount of diesel were comparable.
The effects of methanol and ethanol on a laminar premixed low-pressure (30Torr) n-heptane/toluene flame were investigated by using synchrotron photoionization and molecular-beam mass spectrometry ...techniques. The overall carbon flux was maintained constant (0.6g/min) and the equivalence ratio was kept at 2.0 for all the tested flames. Mole fraction profiles of major and intermediate species including most aromatic species were derived and compared among the flames. Simulations were performed based a multi-fuels kinetic mechanism, and the predicted concentrations of most flame species agree well with the measured results. The addition of alcohol showed negligible chemical effect on the hydrocarbon fuels decomposition. Meanwhile the formation of aromatic hydrocarbon intermediates, particularly of those that formed at the later stages of reaction zone, was significantly inhibited. The kinetic study shows that massive HO2 and OH radicals are induced by alcohol addition at the intermediate-temperature region. Thus, the rate of toluene consumption through hydrogen abstraction increases at this region. For this reason as well as that toluene is partially replaced by alcohol fuels, the toluene consumption rate decreases in the followed high-temperature polycyclic aromatic hydrocarbons (PAHs) formation region, which leads to the more significant decrease in PAHs production rates due to the amplification effect of combination reactions in PAHs formation. Such phenomenon indicates that the introduction of alcohol could significantly restrain the formation of aromatic hydrocarbons.
This paper introduces a Diesel/methanol compound combustion system (DMCC) and its application to a naturally aspirated Diesel engine with and without an oxidation catalytic converter. In the DMCC ...system, there are two combustion modes taking place in the Diesel engine, one is diffusion combustion with Diesel fuel and the other is premixed air/methanol mixture ignited by the Diesel fuel. Experiments were conducted on a four cylinder DI Diesel engine, which had been modified to operate in Diesel/methanol compound combustion. Experiments were conducted at idle and at five engine loads at two levels of engine speeds to compare engine emissions from operating on pure Diesel and on operating with DMCC, with and without the oxidation catalytic converter. The experimental results show that the Diesel engine operating with the DMCC method could simultaneously reduce the soot and NOx emissions but increase the HC and CO emissions compared with the original Diesel engine. However, using the DMCC method coupled with an oxidation catalyst, the CO, HC, NOx and soot emissions could all be reduced.
The super-knock poses new challenges for further increasing the power density of spark ignition (SI) engines. The critical factors and mechanism connecting regarding the occurrence of super-knock are ...still unclear. Misfire is a common phenomenon in SI engines that the mixture in cylinder is not ignited normally, which is often caused by spark plug failure. However, the effect of misfire on engine combustion has not been paid enough attention to, particularly regarding connection to super-knock. The paper presents the results of experimental investigation into the relationship between super-knock and misfires at low speed and full load conditions. In this work, a boosted gasoline direct injection (GDI) engine with an exhaust manifold integrated in the cylinder head was employed. Four piezoelectric pressure transducers were used to acquire the data of a pressure trace in cylinder. The spark plugs of four cylinders were controlled manually, of which the ignition system could be cut off as demanded. In particular, a piezoelectric pressure transducer was installed at the exhaust pipe before the turbocharger to capture the pressure traces in the exhaust pipe. The results illustrated that misfires in one cylinder would cause super-knock in the other cylinders as well as the cylinder of itself. After one cylinder misfired, the unburned mixture would burn in the exhaust pipe to produce oscillating waves. The abnormal pressure fluctuation in the exhaust pipe was strongly correlated with the occurrence of super-knock. The sharper the pressure fluctuation, the greater the intensity of knock in the power cylinder. The cylinder whose exhaust valve overlapped with the exhaust valve of the misfired cylinder was prone to super-knock.
This paper presents the concept of a diesel methanol compound combustion (DMCC) system and some experimental results on the application of the system to two diesel engines. In the DMCC system, diesel ...fuel is used for engine starting and for low load operation. At medium to high load, a fixed amount of diesel fuel is maintained while extra energy is acquired by injecting methanol into the intake manifold to form a homogeneous methanol/air mixture. The system was tested on two 4-cylinder diesel engines: one naturally aspirated and the other turbocharged. In both cases, the DMCC is found to reduce brake specific equivalent fuel consumption, reduce smoke emission, and reduce NOx emission but increase CO and HC emissions.
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