Search

Particulate matter (PM) emissions have become an increasingly noticeable concern for gasoline vehicles, especially for gasoline direct injection (GDI) one. The PM index (PMI) model developed by Aikiwa et al. provides an effective model linking the fuel properties to the PM emissions from gasoline vehicles. In this study, a more practical reduced PM index (RPMI) was developed based on the detailed analysis of 22 fuels with various physical properties and chemical compositions. Two approaches of statistical mathematics of correlation analysis and multivariate linear regression (MLR) were adopted in the modeling process. The RPMI involving two global fuel properties of T90 (distillation temperature of 90% by volume) and T70 (distillation temperature of 70% by volume) was tested to be statistically valid. In addition, the model was verified through the engine bench tests and the vehicle emissions tests. The results reveal that the RPMI showed good correlations to the engine-out particle number (PN) emissions under all of the typical test conditions, including PFI (port fuel injection) mode, GDI (gasoline direct injection) mode and compound injection (PFI + GDI) mode. In addition, the RPMI demonstrated a significantly high correlation to vehicle-out PN emissions over the New European Driving Cycle (NEDC) with the determination coefficient R2 = 0.947. Moreover, a moderate correlation (R2 = 0.801) of the index to the filter PM mass emissions was observed. In the light of no additional components analysis is needed except for the legitimate tests of fuels, the RPMI has the potential to be a useful tool for original equipment manufacturers (OEMs) and environmental certification departments to expediently evaluate the fuel effect on PM emissions.

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 ( 1200 μs) induced a simultaneous increase of particles with different size.

Based on European Steady-state Cycle (ESC) test procedure, an engine test was carried out to meet the demand of Euro V legislation with diesel methanol compound combustion (DMCC) technology on a common-rail, turbocharged, inter-cooling heavy-duty and high pressure exhaust gas recirculation (HP EGR) diesel engine with meeting the requirements of Euro IV legislation. The engine was just modified with DMCC technology and combined with after-treatment device diesel oxidation catalyst coupled with particulate oxidation catalyst (DPOC). The test results show that it can fully meet the demand of Euro V legislation without the help of selected catalyst reduction (SCR). Additionally, the comparative analysis of the dynamic and economic performances between the DMCC Euro V engine and the baseline Euro IV engine was presented in this study. The regulated emissions (included HC, CO, NOX, PM (particulate matter)) and unregulated emissions (included formaldehyde (HCHO) and unburned methanol (CH3OH)) before and after DPOC from DMCC Euro V engine were also investigated. The dynamic performance of DMCC Euro V engine is basically consistent with the baseline Euro IV engine, while there is a slight deterioration in economic performance at certain operation conditions in terms of calorific value. Compared with the baseline engine before DPOC, the DMCC engine causes an increase in HC, CO, HCHO and CH3OH emissions, but the NOX and PM emissions are much better. The DPOC efficiency in the conversion rate of HC, CO, HCHO and CH3OH is over 98% under the whole ESC test procedure, and for PM, the conversion efficiency is only around 21%. However, DPOC has no obvious influence on the conversion of NOX emissions.

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 (CO 2 ), nitrous oxide (N 2 O), unburned methanol (CH 3 OH), formaldehyde (HCHO), formic acid (HCOOH), 1,3-butadiene (1,3-C 4 H 6 ), benzene (C 6 H 6 ) and toluene (C 7 H 8 )) 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 CO 2 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.

The methanol fuel used in diesel engine can reduce the emissions effectively, while the performance of engine keeps unchanged or even improved, the study of methanol used in diesel engine is paid more and more attention. Experiments were conducted in a 4-cylinder, turbocharged direct injection diesel engine fueled with diesel/methanol dual fuel (DMDF). In the experiment, methanol was injected into inlet duct by two low-pressure injectors, and directly mixed with intake air before entering the engine. The diesel fuel was directly injected in cylinder. The methanol substitution percent (MSP), intake air temperature and engine speed were changed to investigate the unevenness degree (UED) cylinder-to-cylinder. The experimental results show that the UED of engine increases with the increase of MSP under various engine loads, the COV pp increases with MSP under low engine load, and the COV pp curves vary very little under low MSP under 75% and 100% engine load, but a significantly rise appeared when MSP further increases. The UED gradually increases with the increase of intake air temperature, and it is usually less than 8% when intake air temperatures lower than 80 °C under 40% MSP. It suggests it is helpful to decrease the UED when the intake air temperature is in the range of 35–80 °C as MSP less than 40%. In addition, the difference of pressure between cylinder-to-cylinder decreases with the increase of engine speed, it can be considered raising MSP at high engine speed in order to gain better engine economy.

An experimental study was conducted to investigate into the cyclic variations of diesel methanol dual fuel (DMDF) combustion on a methanol fumigated diesel engine. The effects of engine load, methanol substitution percent (MSP), injection timing and intake temperature on cyclic combustion variation were studied experimentally. In-cylinder pressure of 100 consecutive combustion cycles were recorded for each test case. The coefficient of variation (COV) of maximum in-cylinder pressure ( p max ), maximum mass-averaged temperature ( T max ) and the indicated mean effective pressure (IMEP) were used to evaluate the cyclic variations of DMDF combustion. The results showed that the stability of DMDF combustion at high loads is comparable with that of neat diesel combustion. But the magnitude of cyclic DMDF combustion variations increases at light loads and more sensitive to the quantity of fumigated methanol. At light loads, COV p max and COV T max increase significantly and the crank angles corresponding to p max and T max scatter more around with the increment of MSP. IMEP values show obvious fluctuations and are distributed in a wider range with an increase in MSP. DMDF combustion stability is very sensitive to intake temperature. At light loads the COVs of all combustion parameters decrease with the increment of intake temperature. In contrast, at high loads, the effect of intake temperature on the cyclic variations is quite small while there is a significant increase in the COVs when the intake temperature exceeds over 75 °C. Overall, injection timings does no effect on cyclic variations of DMDF combustion.

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.

Diesel–methanol dual fuel (DMDF) engines at light loads suffer from low thermal efficiency and high unburned percentages of fuel. Pilot fuel injection timing and intake temperature are two important parameters which affect the combustion process in DMDF engines. In present experimental work, the combined effects of intake temperature and injection timing on the performance of a DMDF engine have been studied. The experiments were conducted on a methanol-fumigated diesel engine at 25% of full load and the results concerning performance, combustion characteristics and emissions were analyzed. Results show that the low efficiency at light loads can be improved significantly by raising the intake temperature and advancing the injection timing of direct-injected diesel. Increasing the intake temperature also significantly decreases the heat release rate of premixed combustion and increases the combustion rate of methanol burned by flame propagation. Flame propagation of the methanol–air mixture disappears gradually and DMDF combustion transforms into single stage combustion as the injection timing is retarded. When injection timing is retarded after 4.6° crank angle, misfire occurs at higher methanol substitute percent (MSP) and lower intake temperature, while the auto-ignition of methanol occurs at lower MSP and higher intake temperature. Under DMDF operation, soot and nitrogen oxides trade-off dilemma is completely broken at lower intake temperature and higher MSP.