Diesel Methanol Dual Fuel Engine Research Articles

Study on the active regeneration characteristics of DPF in diesel-methanol dual-fuel engine under different exhaust oxygen concentrations

This study proposes a method to control exhaust oxygen (O2) concentration by adjusting the intake throttle valve, achieving intake throttling, and reducing intake airflow. The impact of exhaust O2 concentration at the inlet of the diesel oxidation catalyst (DOC) the diesel particulate filter (DPF) performance during active regeneration in diesel engines is investigated. Experiments are conducted under methanol substitution rates (MSR) of 0% and 20% to investigate how different exhaust O2 concentrations affect the performance of the DOC and DPF during active regeneration. A comparative analysis of fuel consumption and cumulative CO2 emissions during DPF active regeneration under different exhaust O2 concentrations is performed. Research results indicate that decreasing exhaust O2 concentration reduces exhaust flow, raising DOC inlet temperature. This enhancement improves catalytic conversion efficiency, accelerating the rise in DPF inlet temperature. The average conversion efficiency of DOC to unburned methanol exceeds 98.07%. After initiating DPF active regeneration, O2 concentration sharply drops, leading to elevated CO2 emissions. As soot combustion advances, the required O2 diminishes, resulting in a gradual rise and eventual stabilization of O2 emissions. Economically and environmentally, irrespective of MSR (20% or 0%), there exists an optimal exhaust O2 concentration that minimizes effective regeneration time during DPF active regeneration, achieving minimal fuel consumption and the lowest CO2 mass emissions. This study offers theoretical support for optimizing energy-saving and emission-reduction processes during DPF active regeneration.

Investigation of the impacts of regeneration temperature and methanol substitution rate on the active regeneration of diesel particulate filter in a diesel-methanol dual-fuel engine

Methanol (CH3OH), a sustainable fuel derived from many renewable resources, simultaneously reduces nitrogen oxides (NOx) and particulate matter (PM) in diesel-methanol dual-fuel engines. This study systematically investigated the effects of regeneration temperature and methanol substitution rate (MSR) on the performance of diesel oxidation catalyst (DOC), diesel particulate filter (DPF), and the temperature characteristics of DPF substrate during active regeneration. The experimental results show that the DOC catalytic oxidation of unburned CH3OH has a conversion rate of more than 97.5 % across various MSR. DPF inlet temperature rose faster with higher MSR. Elevated regeneration temperature reduced effective regeneration times and diesel equivalent consumption. Within active regeneration conditions with MSR increases, both effective regeneration times and diesel equivalent consumption initially decreased and then increased as the MSR rose. At MSR = 30 %, the duration of effective regeneration times during DPF active regeneration was minimized, and diesel equivalent consumption at MSR = 30 % experienced an improvement of 22.52 % compared to MSR = 0 %. The highest DPF substrate temperatures across various MSR levels are consistently observed at T6 position within the DPF. This study can provide a theoretical basis for the active regeneration of DPF in methanol-diesel dual-fuel mode.

Numerical investigation and experimental validation on the leakage of methanol and formaldehyde in diesel methanol dual fuel engine with different valve overlap

The diesel methanol dual fuel (DMDF) engine is confronting with the problem of high unregulated emissions of methanol and formaldehyde. The previous studies on unregulated emissions of DMDF engine focused on the measuring methanol and formaldehyde concentrations in the exhaust without distinguishing whether emissions come from leakage during valve overlap or incomplete combustion in the cylinder. In this study, a computation fluid dynamics (CFD) model coupled with a detailed chemical kinetic mechanism was developed to investigate the methanol and formaldehyde emissions of DMDF engine. The results showed that the unburned methanol and formaldehyde in the cylinder were the main part of the total methanol and formaldehyde emissions based on the 41 °CA valve overlap of simulation model. Then the effects of different intake valve opening (IVO) and exhaust valve closing (EVC) on methanol emissions were investigated. The results showed that only increasing IVO or EVC had very little effect on the leakage of methanol during scavenging. However, when the IVO and EVC changed simultaneously, the valve lift would significantly increase during the valve overlap of scavenging, which had a great impact on methanol leakage. The simulation results were validated by experiments in a 6170 marine engine. The experimental results were consistent with the simulation results and the increase of effective flow area caused by valve lift during large valve overlap was the most important reason for the increase of methanol emission. Therefore, all engines have almost no leakage in small valve overlap. However, with the increase of valve overlap, the actual results were different due to the different valve lift and mixture concentration of different engines.

Effect of EGR strategy on combustion and emission of DMDF engine for meeting China VI emission legislation

Study on EGR mode and demand were carried out to meet with the requirements of main emission limits of China VI on a diesel methanol dual fuel (DMDF) engine equipped with Hybrid exhaust gas recirculation (EGR) system coupled with back pressure valve (BPV). According to the World Harmonized Steady-State Cycle (WHSC) test cycle, the effects of EGR mode under high methanol energy ratio (MER) on the combustion, emissions and economy of DMDF engines were studied without the help of selected catalyst reduction (SCR). Considering the weight based on WHSC test cycle of full load was only 0.083, and EGR demand of full load was low, the optimal EGR strategy under different loads except full load was determined for DMDF engine. The results demonstrated that through the early injection strategy with high MER, particulate matter (PM) emissions were all at an extremely low level, far below the requirements by legislation limit of 0.01 g/kWh. With the increase of EGR rate, nitrogen oxides (NOx) emissions were significantly reduced under different loads, accompanying with one or more EGR modes at 25%, 50%, and 70% loads to ensure that NOx emission could meet the requirements by legislation limit of 0.4 g/kWh, while PM emissions were at a very low level at the same time. Demand for EGR rate of light loads was generally higher than that for medium loads, but under light loads, each of hybrid EGR modes could meet the demand of China VI legislation. While under medium loads, the dual loop (DL) EGR modes, i.e., both low pressure (LP) and high pressure (HP) EGR mode must be needed. In LP EGR mode combined with back pressure valve (BPV), higher EGR rate was required under the same NOx control target, owing to the higher intake air volume than those of other modes. The trade-off relationship in HP_BPV mode between NOx and PM emissions still existed, and high EGR rate often leaded to an increase in PM.

Effects of diesel pre-injection on the combustion and emission characteristics of a common-rail diesel engine fueled with diesel-methanol dual-fuel

The diesel-methanol dual-fuel (DMDF) combustion was performed on a six-cylinder, common-rail diesel engine. To this end, methanol was premixed with air in the intake pipe and ignited by the directly injected diesel fuel in the cylinder. Single and double injection were considered in this study. Double injection included pre-injection and then main injection. The aim was to investigate, in comparison with the single injection strategy, what effects diesel pre-injection strategy may have on the combustion and emission characteristics of the test DMDF engine. The experiment was carried out at 1400r/min, 50% load and different values of the co-combustion ratio. The results show that, for double injection compared with single injection mode, both the heat release rate and the maximum cylinder temperature become lower, while the cycle-to-cycle variation of indicated mean effective pressure becomes higher. The results of emission characteristics indicate that, under double injection mode, the HC emissions decrease, while those of CO, NOx and PM increase. The NOx emissions and the size of particular matter both increase with co-combustion ratio, when diesel pre-injection was applied.

Exergy loss analysis on diesel methanol dual fuel engine under different operating parameters

In order to reveal the mechanism of high thermal efficiency of diesel methanol dual fuel (DMDF) engine, the exergy loss of DMDF engine under different operating parameters is investigated by using experimental and calculative methods based on the second law of thermodynamics. It has been found that DMDF has lower heat transfer exergy loss under all engine loads due to the high latent heat of vaporization of methanol which reduces the temperature in-cylinder. The exhaust exergy loss of DMDF under high load is relatively low compared with that of pure diesel fuel, while it is opposite to that under medium-low load. This is due to the influence of different temperatures on the incomplete combustion of methanol, which also indicates the main cause for the high thermal efficiency of DMDF under high load. Then studies on exergy analysis of DMDF under different temperatures were carried out. The studies covers the effect of intake air temperature on exergy efficiency, the heat transfer exergy loss and the exhaust physical exergy loss increase with rising intake air temperature as well. The results shows that the exhaust chemical exergy loss decreases significantly with the increase of intake air temperature and higher intake air temperature helps to improve exergy efficiency. Additionally, it is concluded that higher methanol temperature and cooling water temperature can improve exergy efficiency by decreasing exhaust exergy loss and combustion irreversible exergy loss. Finally, some feasible measures are proposed to further improve DMDF engine’s performance.

Selective catalytic reduction of nitrogen oxides with methanol over the (cobalt-molybdenum)/alumina dual catalysts under the diesel methanol dual fuel exhaust conditions

The (cobalt-molybdenum)/alumina ((Co-Mo)/Al2O3) dual catalysts have an excellent performance on the selective catalytic reduction (SCR) of nitric oxide with methanol (methanol-SCR) on the synthetic gas test bench. The catalytic performance of (Co-Mo)/Al2O3 needs to be studied on the engine test bench due to the complicated emissions of engines. Tests were carried out on the diesel methanol dual fuel (DMDF) engine. The effect of methanol supply methods, methanol dosing, injection timings of diesel fuel and exhaust gas recirculation (EGR) ratios on the performance of methanol-SCR was investigated. Results show that the performance of methanol-SCR on the engine test bench slightly deteriorates compared with that on the synthetic gas test bench. The performance of methanol-SCR on the active methanol supply mode is superior to that on the passive methanol supply mode. The low nitrogen oxides (NOX) conversion with passive methanol supply mode suggests that the ratio of carbon monoxide to hydrocarbons (more than 1) and the ratio of nitrogen dioxide to NOX are the critical factors on NOX conversion during the catalyst selection. However, the passive methanol supply mode has less effect on the fuel consumption. The catalytic efficiency of methanol-SCR is improved by the increased methanol dosing and EGR ratios and the retarded injection timings. The methanol dosing increases the particulate emissions and the fuel consumption. Increasing EGR ratios is less bad for the fuel consumption than retarding injection timings. A combination of the DMDF engine and the methanol-SCR realizes the ultra-low NOX emissions.

Strategy of improving fuel consumption and reducing emission at low load in a diesel methanol dual fuel engine

The experiments were performed to achieve a significant reduction in nitrogen oxides (NOx) and soot emissions while achieving no reduction in Brake Thermal Efficiency (BTE) for Diesel Methanol Dual Fuel (DMDF) engine at low load condition. The optimization strategies mainly include internal exhaust gas recirculation (EGR), external EGR, intake air heating and diesel injection timing retarded. NOx and soot emissions, BTE, and combustion characteristics were discussed. Experiments were conducted at 1660 r/min with the output torque 220 N·m, corresponding to 50% of full engine load. The main parameters for evaluating the optimization results include NOx emissions, soot emissions, BTE, Pressure Rising Rate (PRR) and fuel cost. The optimized result of DMDF mode is obviously better than those of diesel mode. The optimization process for DMDF mode weakens the trade-off relationship between key parameters which includes NOx emissions, soot emissions, BTE, PRR and fuel cost. Meanwhile, NOx emissions are significantly lower than those from the baseline diesel mode, which decreases from 9.76 to 1.53 g/kW.h. Soot emissions are almost maintained at the level of the baseline diesel mode. The optimized fuel cost of DMDF mode is greatly improved, and the BTE is slightly higher than that of baseline diesel mode.

Experimental study on energy balance of different parameters in diesel methanol dual fuel engine

Based on the first law of thermodynamics, this paper presents the experimental results of parameter study on energy balance of a diesel methanol dual fuel (DMDF) engine including load characteristic tests for both pure diesel (D) mode and DMDF mode and comparison of energy flow conversion under different load ratios. The results show that replacement ratio keeps decreasing with load increases. In addition, operating parameters, including cooling water temperature, intake air temperature and methanol temperature, were investigated to explore their effects on energy flow distribution in DMDF engine. The results show that increasing intake air temperature has the most important effect on reducing DMDF engine’ s replacement ratio. Besides that, higher cooling water temperature and methanol temperature also contribute to improving DMDF engine’s thermodynamics performance. All these phenomena can be explained by the energy flow transformation when switching to DMDF combustion. On the basis of the above analysis results, some feasible measurements are proposed to further improve DMDF engine’s thermodynamic behavior.

An investigation on the characteristics of and influence factors for NO2 formation in diesel/methanol dual fuel engine

It had been found in previous experimental studies that the compression ignition engine with Diesel/Methanol Compound Combustion (DMCC) could significantly increase nitrogen dioxide (NO2) emission, compared with conventional diesel mode. However, the detailed formation process and influence factors of NO2 in Diesel/Methanol Dual Fuel (DMDF) engine have not been reported previously. In order to investigate the mechanism of increased NO2 and effect factors of NO2 emission, following works were conducted: Firstly, in light of the literature researches, a hypothesis concerning the NO2 formation procession in DMDF engine was presented, whose demonstration was realized by using numerical simulation; Secondly, the experiments about the effect of methanol substitute proportion (MSP), exhaust gas recirculation (EGR) and exhaust backpressure on the NO2 emission were conducted, whose results were analyzed by using the proved hypothesis. The results of simulation justified that compared with diesel case, the existence of methanol premixed region in DMDF mode was the main cause of increased NO2, and the impact of temperature on the NO2 emission mainly lay in that of temperature on hydroperoxyl (HO2) radicals. The experiments showed that along with the increase of MSP, NO2 emission increased firstly and then decreases. The addition of EGR could lead to the reduction of NO2, while the slight increase of exhaust backpressure would increase total nitrogen oxides (NOX) emission.

Effect of diesel late-injection on combustion and emissions characteristics of diesel/methanol dual fuel engine

The late-injection strategy (close after main-injection) of common-rail diesel engine is capable of enhancing combustion turbulence and reducing particulate matter (PM) emissions. In this work, experimental study was performed to investigate the effect of diesel late-injection on combustion and emissions characteristics of diesel/methanol dual fuel (DMDF) engine. The experiments were carried out at a constant engine speed of 1340 rpm and a medium load of 1.0 MPa brake mean effective pressure (BMEP) with various methanol substitution ratio (MSR) on a common rail DMDF engine. The results reveal that higher MSR caused simultaneous decrease of nitric oxides (NOx) and accumulation mode PM emissions in spite of late-injection strategy. In particular, an augment of up to 12.8% in nucleation mode particle number (PN) was observed as MSR increased from 15% to 50%. A small late-injection of diesel (<7.5 mg/cycle) had little impact on in-cylinder pressure and heat release rate (HRR). However, enhanced or retarded late-injection led to a decline in peak gas mean temperature (GMT) but an increase in later combustion temperature. With late-injection quantity (LIQ) increased from 1.5 mg/cycle to 7.5 mg/cycle, both NOx and accumulation mode PM decreased. Meanwhile, nucleation mode PM was almost unchanged and even rebounded slightly with overmuch LIQ (7.5 mg/cycle) in DMDF mode. Retarded late-injection led to a continuous reduction of 12.9% at most in NOx emissions in DMDF operation. As the interval between main-late injections (MLII) increased from 800 μs to 1200 μs, a trade-off relation appeared between nucleation mode and accumulation mode particles due to the mutual transformation of them. Furthermore, too delayed late-injection (MLII > 1200 μs) induced a simultaneous increase of particles with different size.

To extend the operating range of high MSP with ultra-low emissions for DMDF unit pump engine

Experiments were conducted to extend the operation range of Diesel/Methanol Compound Combustion (DMCC), as to further reduce the emissions of Diesel Methanol Dual Fuel (DMDF) engine at full load. The engine was operated under 100% of full engine load at three different speeds of 1660 r/min (speed A), 2090 r/min (speed B), and 2520 r/min (speed C), respectively, as well as 75% of full load at the speed of 1660 r/min. At full load, the results showed that the methanol substitution for diesel proportion (MSP) of DMDF engine could be greatly extended to 80% by using suitable combustion control strategy, which was restricted less than 15% in the previous study. Simultaneously, the knock tendency was reduced into an unobservable magnitude at such a high MSP. Furthermore, the nitrogen oxides (NOx) emission could be significantly reduced, and the lowest NOx emission was down to 1.25 g/kW.h at MSP73 under A75 test point. Meanwhile, the soot emission could be reduced to ultra-low level when the diesel fuel injection duration is shorter than the ignition delay of diesel combustion. The lowest soot emission is decreased to 0.004 g/kW·h at MSP72 under B100 test point, which is lower than the requirement of EURO VI limitation. The results demonstrated that methanol has the advantage of smokeless and flameless while burning, thus soot production could be reduced when the engine fueled with more methanol fuel. The testing results also showed that the total hydrocarbons (THC) and the carbon monoxide (CO) emissions are increased with increasing MSP.

Comparison of the conversion efficiency of DOC and DPOC to unregulated emissions from a DMDF engine

The experimental research on reducing unregulated emissions (included unburned methanol, formaldehyde, formic acid, 1,3-butadiene, benzene and toluene) of diesel/methanol dual fuel (DMDF) engine with different after-treatment devices was carried out on a turbocharged inter-cooling diesel engine. The DMDF engine was operated under 25%, 50%, 75% and 100% of full load at the engine speed of 1660rpm and 2090rpm with the same injection parameters for the different methanol substitution ratios (MSR). Unregulated emissions of DMDF engine with and without after-treatment devices single diesel oxidation catalyst (DOC) and DOC coupled with particulate oxidation catalyst (DPOC) were studied in comparison. The results show that compared with pure diesel mode, the unregulated emissions tested in this research are all increased in different degrees when the engine operates on diesel/methanol dual fuel mode, and they are all increased with increasing fumigation methanol. The conversion efficiency of DPOC for unregulated emissions tested in this research is higher than that of single DOC. Single DOC could significantly reduce the unburned methanol, 1,3-butadiene and formic acid emissions from DMDF engine, especially at medium and high load when exhaust gas temperature is relative high, but formaldehyde emissions after DOC are increased at low load. After the catalytic oxidation of DPOC, the unburned methanol, formaldehyde, formic acid, benzene and toluene emissions of diesel/methanol dual fuel mode under all load at the speed of 1660rpm, all except low load at the speed of 2090rpm are not much different from pure diesel mode.

Effects of co‐combustion ratio on rapid combustion, cyclical variation, and emissions of a heavy‐duty diesel engine fueled with diesel‐methanol dual‐fuel

Diesel‐methanol dual‐fuel (DMDF) combustion was achieved on a 6‐cylinder, heavy‐duty, turbocharged and common‐rail diesel engine. In DMDF mode, the coal‐produced methanol is induced to the upstream of the intake manifold and premixed with the fresh air to form a homogeneous methanol‐air mixture and then ignited by direct‐injected pilot diesel in cylinder. The purpose of this study is to investigate the effects of co‐combustion ratio (CCR) on the rapid combustion, cyclical variation and emissions of the DMDF engine. The experimental results show that CCR affect the rapid combustion (α) and knock tendency (β) greatly. With CCR increasing, both α and β increase significantly. The β exhibits an obviously large value under heavy load although CCR and α are small. At larger CCR, DMDF mode may generate a seriously cyclical variation and the coefficient of variation for indicated mean effective pressure (COVIMEP) exhibits a relatively large value. However, with engine load increasing, the cyclical variation can be obviously decreased. It is also shown that both NOx and smoke emissions in DMDF mode present an obviously decrease trend, while CO and HC emissions exhibits an increase trend. A further reduction of NOx and smoke emissions can be obtained by increasing CCR, but CO and HC emissions are increased in this case. © 2017 American Institute of Chemical Engineers Environ Prog, 36: 1528–1536, 2017

Numerical study of the performance and NOx emission of a diesel-methanol dual-fuel engine using multi-objective Pareto optimization

The effect of methanol addition on the performance and NOx emission of a diesel engine was investigated using one-dimensional engine cycle simulation. The methanol component was injected into the intake manifold of a diesel engine at a certain energy fraction (0, 5, 10, or 15%) of the fuel. The in-cylinder pressure and temperature decreased as the methanol content increased due to the lower cetane number and lower heating value of methanol. The resulting decrease in the combustion efficiency lowered the NOx emission and brake thermal efficiency of the engine, and consequently deteriorated the brake specific fuel consumption (BSFC). The BSFC decreased but the NOx emission increased with advanced injection timing under dual-fuel operating conditions. Response surface plots of the BSFC and NOx emission as a function of the injection timing and exhaust gas recirculation (EGR) rate were obtained using a design of experiment method. The optimal Pareto fronts that improved both the BSFC and NOx emission were found. The EGR rate had a greater influence on the optimal Pareto front than the injection timing, which suggested that design parameters such as the injection timing and EGR rate could be used to control the performance and emission under various duel-fuel conditions.

Experimental investigations of the effects of pilot injection on combustion and gaseous emission characteristics of diesel/methanol dual fuel engine

A diesel engine with 6-cylinder, turbocharged intercooling and common rail system was modified to operate on diesel/methanol dual fuel (DMDF). To optimize combustion process at high methanol substitution ratio (MSR) and further decrease exhaust emissions of DMDF engine at low load condition, pilot injection strategy was applied on it and the combustion, regulated and unregulated gaseous emission (included NOx, CO, THC, carbon dioxide (CO2), nitrous oxide (N2O), unburned methanol (CH3OH), formaldehyde (HCHO), formic acid (HCOOH), 1,3-butadiene (1,3-C4H6), benzene (C6H6) and toluene (C7H8)) characteristics were experimentally investigated. Experimental results reveal that the application of pilot injection could improve combustion stability and fuel economy at high MSR, and it can also reduce regulated emissions CO, THC except NOx, and unregulated emissions tested in this study except CO2 on M0 and M10 mode and toluene on M50 mode when compared with single injection cases. Increase pilot injection quantity and advance pilot injection timing both cause an increase in in-cylinder temperature and pressure before main combustion. The variations of pilot injection quantity and timing have less effect on regulated and unregulated gaseous emissions except NOx on M0 and M10 mode than higher MSR mode. With the rise of pilot quantity and the advance of pilot injection timing, HC and CO emissions decrease gradually but NOx emissions ascend; almost all unregulated emissions tested in this study on M30 mode reduce gradually; but when the MSR continues to rise to 50%, increasing emissions in unburned methanol, 1,3-butadiene and benzene are observed.

Mechanistic Study of Ignition Characteristics of Diesel/Methanol and Diesel/Methane Dual Fuel Engine

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.

Effects of diesel injection parameters on the rapid combustion and emissions of an HD common-rail diesel engine fueled with diesel-methanol dual-fuel

The diesel-methanol dual-fuel (DMDF) combustion mode is performed on a 6-cylinder, heavy duty (HD), common-rail diesel engine. In DMDF mode, the methanol is premixed with air in the intake pipe and afterwards ignited by the direct-injected diesel in cylinder. This study is aimed to investigate the effects of diesel injection parameters on the rapid combustion and emissions of the DMDF engine. The experimental results show that the diesel injection parameters affect rapid combustion fraction (α) greatly, which increases as the diesel injection pressure rises while decreases as the diesel injection timing advanced or diesel injection quantity increases. The roar-combustion level of the DMDF engine is mainly controlled by the heat release rate (HRR) of rapid combustion phase. Both increasing the diesel injection pressure and advancing the diesel injection timing are beneficial to intensify roar-combustion level, but it can be weakened by increasing diesel injection quantity. Compared with original diesel combustion mode (D mode), NOx and smoke emissions in DMDF mode are all reduced, while CO and HC emissions increased obviously. Smoke emission can be further reduced by coupling the high diesel injection pressure and the advanced diesel injection timing. However, NOx emission may be increased in this case.

Effects of rapid burning characteristics on the vibration of a common-rail diesel engine fueled with diesel–methanol dual-fuel

The diesel–methanol dual-fuel (DMDF) combustion mode is conducted on a six-cylinder, turbo-charged, inter-cooled diesel engine. In DMDF mode, methanol is injected into the intake pipe to premix methanol and air, and then ignited by the direct-injected diesel in cylinder. This study is aimed to investigate the effects of rapid burning characteristics on the vibration performance of the DMDF engine. The experimental results show that the combustion process of the DMDF engine can be divided into two phases. The rapid burning characteristics, the centroid angle of rapid burning (α) and the rapid burning fraction (β) have important influence on the vibration characteristics of the DMDF engine. The co-combustion rate (CCR) and engine load affect β greatly, and diesel injection timing also affects α and β greatly. However, the diesel injection pressure has little effect on rapid burning characteristics. By means of optimized diesel injection timing and pressure, the vibration can be reduced and the peak value of CCR can be increased.

Theoretical and experimental investigations on energy balance on DMDF engine

This paper presented the analytical results for the energy balance of a diesel methanol dual-fuel (DMDF) engine. A methanol injection system was fixed on a diesel engine and let the engine to alternate to run in either the pure diesel (D) mode or DMDF mode. Primary application of the thermal balance analysis was to investigate the cause of methanol replacement ratio SR changing with engine loads. Calculations were conducted within the control volume by comparing each of the energy terms. The results show that the reduction in cooling loss in DMDF mode is the dominant factor for low SR at high loads. While, a substantial increase in incomplete combustion loss in DMDF mode is the most important reason for high SR at low loads. Another application of the thermal balance analysis was to research the cooling loss in DMDF mode which implied unique characteristics. Therefore, the changing methanol replacement rate SP experiments were carried out in various engine loads, giving the results that the cooling loss in DMDF mode is always lower than that in D mode, and it goes even lower as SP rises. Finally, the effect of methanol temperature on SR was also investigated from the thermal balance point of view. The results reveal that the incomplete combustion loss decreasing in higher methanol temperature conditions will lead to a certain extent of SR drop. All these results are related to the energy flow distribution within the engine.