Methanol Substitution Research Articles

Parametric study of combustion characteristics of diesel/methanol dual fuel engine using global sensitivity analysis and multi-objective optimization

The pursuit of clean and efficient internal combustion engine power necessitates the substitution of fossil fuels with methanol and the adoption of advanced combustion strategies. This study examines the combustion and emission characteristics of methanol/diesel dual-fuel compression ignition engines. To understand the intricate interplay between critical parameters and engine performance, the global sensitivity analysis (GSA) method is employed, utilizing Sobol sensitivity as the quantitative metric. The investigated parameters include methanol substitution rate, diesel injection parameters, and five thermodynamics parameters concerning in-cylinder conditions. A validated computational fluid dynamics (CFD) model, coupled with a chemical kinetic mechanism, is developed to predict the combustion behavior of the dual-fuel engine accurately. This predictive capability forms the basis for utilizing the tree-based process optimization (TPOT) algorithm. By implementing TPOT, a significant reduction in the mean square error (MSE) of the predicted characteristics model is achieved, averaging a decrease of 73.59 %. Subsequently, a multi-objective optimization is conducted, exploring the impact of varying target weights on the optimal outcomes. Results show the initial pressure significantly impacts the engine's economy, power and emission characteristics, and NOx formation should be carefully considered in the combustion optimization of dual-fuel engines.

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.

Influence of critical parameters on combustion and emission characteristics of methanol/diesel dual fuel compression combustion engine

Replacing fossil fuels with clean fuels as power sources is an effective method to reduce greenhouse gas and pollutant emissions, and methanol is a potential solution due to its excellent physical and chemical properties. The study comprehensively investigated the influences of the methanol substitution ratio (Rm), three initial cylinder parameters, and three diesel injection parameters on the combustion and emission characteristics of a methanol/diesel dual fuel compression combustion engine. A CFD model coupling with the reaction mechanism for a dual-fuel engine was established and fully verified. The results indicate that methanol substitution for diesel benefits emissions reduction at low load and improves fuel economy at high load. Delaying the diesel injection time and increasing the diesel injection duration time deteriorate fuel economy but reduce NOx emissions. Soot and NOx emissions exhibit a sudden change at a diesel injection angle of 70°. Increasing the initial temperature of the combustion chamber promotes combustion while increasing the initial pressure improves fuel economy. The effect of the initial swirl ratio is mainly observed at low load, where an increase in the initial swirl ratio improves fuel economy, reduces ringing intensity (RI), and lowers soot emissions. The conclusion of this article will guide the development of clean power sources.

Multi-objective optimization of the performance for a marine methanol-diesel dual-fuel engine

Marine methanol-diesel compound combustion (DMCC) engines have received extensive attention in the shipping industry. This work aims to further improve the performance and evaluate the carbon reduction potential of the marine DMCC engine. First, the computational fluid dynamic model of the dual-fuel engine was built. Then, an intelligent regression method based on the grey wolf optimizer (GWO) algorithm optimized support vector machine regression (SVR) was proposed. The methanol substitution rate (MSR), excess air ratio (EAR), and diesel injection timing (DIT) were adopted as the decision variables to establish the regression models for NOx, CO, and CO2 emissions and indicated specific fuel consumption (ISFC). Subsequently, a multi-objective grey wolf optimizer (MOGWO) and entropy weight TOPSIS were employed to obtain the optimal case for achieving low NOx and CO emissions and ISFC. Finally, the maximum MSR was explored to achieve greater carbon reduction benefits while balancing the NOx emission and ISFC. The results showed that after GWO optimization, the coefficients of determination of the SVR regression models are all greater than 0.95, with mean square errors consistently below 0.015. It indicates that the regression models have excellent consistency and applicability. The optimal case calculated by MOGWO and entropy-weighted TOPSIS enables co-optimization of the NOx emission and ISFC while maintaining the CO emission below 600 ppm. Compared to the original case, the optimal case achieves reductions of 26.22 % for NOx and 13.39 % for ISFC. The exploration of the maximum MSR reveals that in the Pareto optimal set, the maximum MSR reaches 56.16 %, at which point the NOx and CO2 emissions reduce by 75.85 % and 59.32 % respectively, while the ISFC increases by 21.67 % compared to the original case.

Effects of diesel injection timing and methanol substitution ratio on combustion and exhaust emission characteristics of a dual fuel compression ignition engine

Effects of diesel injection timing and methanol substitution ratio on combustion and exhaust emission characteristics of a dual fuel compression ignition engine

Effects of methanol substitution rate on combustion and emission characteristics of methanol/diesel dual fuel engines

Effects of methanol substitution rate on combustion and emission characteristics of methanol/diesel dual fuel engines

Numerical study of injection strategies for marine methanol/diesel direct dual fuel stratification engine

To explore the application potential of renewable methanol and direct dual fuel stratification (DDFS) technology in marine internal combustion engines, this study conducted a fuel injection strategy research based on performance optimization for a marine methanol/diesel DDFS engine under high methanol substitution rate (95%). The results show that the fuel mixing process plays a crucial role in methanol/diesel DDFS engine combustion state switching. Premature methanol injection under methanol single-stage injection strategy causes ringing intensity (RI) to exceed the engine limit. Additionally, when start of diesel injection (SOID) occurs earlier than start of methanol injection (SOIM), the shorter methanol/diesel injection interval (MDI) leads to the deterioration of diesel premixed combustion for reason of methanol spray interference. Therefore, adopting an injection strategy with SOID earlier than SOIM under methanol single-stage strategy combined with an appropriately extended MDI achieves better comprehensive engine performance. Further optimization of methanol/diesel DDFS engine using a methanol two-stage injection strategy shows that the methanol two-stage injection strategy provides better fuel economy while maintaining acceptable RI. By increasing the methanol pre-injection ratio (MR1) and optimizing the methanol two-stage injection interval (MMI), the engine economy was further enhanced. Compared with the methanol single-stage injection strategy, the optimized methanol two-stage injection strategy reduced equivalent indicated specific fuel consumption (EISFC) by 3.95%. However, it should be noted that the combustion completeness under the methanol two-stage injection strategy decreased, leading to higher emissions of HC, CO and soot. On the other hand, this strategy resulted in lower NOX emissions due to more sufficient premixed combustion.

Experimental Investigation of the Performance and Unburned Methanol, Formaldehyde, and Carbon Dioxide Emissions of a Methanol-Diesel Dual-Fuel Engine

In the context of global efforts to pursue carbon neutrality, the methanol-diesel reactivity controlled compression ignition (RCCI) combustion has become a promising strategy for diesel engines to reduce emissions with higher thermal efficiency. To further improve the fuel economy of the methanol–diesel RCCI engine and reduce its unregulated emissions, the effects of methanol substitution rate (MSR) and exhaust gas recirculation (EGR) on fuel economy, CO2, MeOH, and H-CHO emissions at different engine speed and load conditions were tested. The conversion efficiency of a conventional diesel oxidation catalyst (DOC) in oxidizing the unregulated emissions under the World Harmonized Steady-State Cycle (WHSC) was also evaluated. The results showed that running the engine in methanol-diesel RCCI mode can significantly improve fuel economy at medium to high loads [greater than 1.18 MPa brake mean effective pressure (BMEP)]. The equivalent brake specific fuel consumption (ESFC) in the RCCI mode was lower than that of the baseline CDC mode, and the utilization of EGR can further improved fuel economy at lower load conditions. The MeOH and H-CHO emissions increased as the MSR increased, and they decreased as the load level and EGR rate increased. The CO2 emissions decreased as the MSR increased, but they increased as the EGR rate increased. The conversion efficiencies of DOC for MeOH, H-CHO and aromatic hydrocarbons (AHC) were around 93%, 84%, and 61%, respectively, under the WHSC test. Exhaust after-treatment by DOC is an effective solution to reduce unburned MeOH and H-CHO from methanol-diesel dual-fuel engines, and to extend RCCI operating range.

Study of Diesel/Methanol Dual Fuel Combustion in CI Engines and Its Practice in China

Article Study of Diesel/Methanol Dual Fuel Combustion in CI Engines and Its Practice in China Anren Yao 1, and Chunde Yao 2,* 1 School of Environmental Science and Technology, Tianjin University, Tianjin 300072, China 2 State Key Laboratory of Engines (SKLE), Tianjin University, Tianjin 300072, China * Correspondence: arcdyao@tju.edu.cn Received: 22 October 2022 Accepted: 21 December 2022 Published: 8 February 2023 Abstract: In order to release the pressure of energy safety from the dependence on oil supplies from overseas, methanol playing an important role as an alternative fuel in the automotive industry in China. At present time, methanol has been widely used as a fuel additive in spark ignition (SI) engines and industrial utilities in many fields. However, it is rarely applied to compression ignition (CI) engines due to its low cetane number, low vaporization rate as well as low solubility with diesel. Therefore, there is a great challenge in using methanol as fuel in CI engines since those engines are the main power units for most heavy-duty vehicles and construction machines as well as marine power units. Through many years of studies by our group, a strategy of diesel/methanol compound combustion (DMCC) was developed, which made methanol be able to apply to CI engines. The engines with DMCC could use diesel/methanol compound with methanol substitution ratio up to 50% for new engines and 30% for the used ones on applications of heavy duty vehicles, construction machines as well as marine power units. In this paper, the strategies of DMCC and the diesel/methanol dual fuel (DMDF) combustion working in CI engines at high and medium speeds are introduced, and the studies that we had done for DMCC and DMDF are reviewed based on their fundamental researches like ignition and combustion, experimental results on bench and field tests, many application examples such as on heavy duty vehicles, construction machines, and boats as well as locomotives.

Substitution of liquid methanol with methanol vapour increases the activity and stability of carbon-based solid acid catalysts in biodiesel production process

The effect of methanol vapour esterification (MVE) on the catalyst activity and reusability was investigated using methanol vapour (MV) instead of liquid methanol for the esterification reaction of oleic acid catalysed by a carbon-based solid acid catalyst (CSAC) S150-4. The conversion yield for the MVE was 98.8 % at a catalyst loading of 4 wt%, methanol/oleic acid molar ratio of 40:1, reaction temperature of 76 °C and reaction time of 4 h. When the catalyst loading is increased to 10 wt%, S150-4 repeatedly catalysed MVE up to the eighth batch, while still achieving 83.4 % conversion. The turnover frequency and number of catalyst reuses were twice as high for MVE as in liquid methanol esterification (LME) under the optimal esterification conditions for both modalities. When compared to LME, MVE achieved a combination of a large amount of methanol and oleic acid in a short time, increasing the conversion yield while reducing the average contact time between methanol and the acidic groups on the surface of the CSAC, resulting in less leaching and chemical derivatization of the sulphonic acid groups from the catalyst in MVE. The production cost of methyl oleate in MVE was 19.1 % lower than that for LME. Therefore, the application of MVE as an alternative to conventional esterification is an effective way to extend the life of CSACs.

Diesel/methanol dual-fuel combustion: An assessment of soot nanostructure and oxidation reactivity

The use of renewable methanol partly substituting diesel fuel can support the transition to low-carbon engines, in the form of diesel/methanol dual-fuel combustion. Particulate filters are still required for diesel/methanol dual-fuel combustion engines to meet the emission standard. Their periodical regeneration depends on the soot oxidation reactivity and nanostructure. We therefore assessed the influences of premixing methanol on soot oxidation reactivity and nanostructure at both engine loads. The results showed that increasing methanol substitution ratio shifted thermogravimetric profiles towards low temperature direction. The average activation energies of M20 and M40 samples (the methanol substitutions of 20% and 40%) dropped by 41.1–43.9 kJ/mol and 53.2–99.7 kJ/mol compared to diesel one at both engine loads, respectively. With an increase in methanol substitution ratio, a notable reduction in primary particle size was observed, with the shorter and more tortuous fringes as well as larger separation distance between the stacked fringes. The increasing trend in soot oxidation reactivity with methanol addition correlated well with the changes in primary particle size and fringe parameters, which means that soot oxidation reactivity highly depends on its morphology and nanostructure. It can be expected from the results that diesel/methanol dual-fuel operation has the advantages in engine fuel economy improvement regarding the regeneration of particulate filters.

Experimental investigation on combustion characteristics and influencing factors of PODE/methanol dual-fuel engine

PODE/methanol dual-fuel combustion mode was conducted on a four-cylinder common-rail engine with PODE direct injection and methanol intake fumigation. This study is aimed to investigate the effects of methanol substitution ratio (MSR), injection timing and inlet temperature on in-cylinder combustion, emission characteristics and fuel economy of dual-fuel engine. Results show that with the increase of MSR, the ignition delay of dual-fuel engine is prolonged, and the COV increases. At medium and small loads, the peak combustion pressure decreases, and the combustion phase is delayed. At high load, the peak values of heat release rate and combustion pressure increase, combustion duration is shortened, and slight knock occurs at 40% MSR. Dual-fuel mode has benefits in reduction of NOx and soot, while increases NO2 and HCHO emissions. With the delay of injection timing, combustion duration is first prolonged and then shortened. The excessive delay of injection timing leads to increased fluctuation of combustion pressure, and partial misfire occurs. With the increase of inlet temperature, the peak values of heat release rate and combustion pressure increase significantly, combustion duration is shortened, and the COV increases. At the inlet temperature of 65 °C, methanol spontaneous combustion occurs near TDC, and thermal efficiency increases to 44.6%.

Effects of EGR combined with DOC on emission characteristics of a two-stage injected Fischer-Tropsch diesel/methanol dual-fuel engine

Fischer-Tropsch (F-T) diesel and methanol are widely regarded as promising clean alternative fuels for engines. The emergence of reactivity controlled compression ignition (RCCI) combustion mode provides new approaches to the application of F-T diesel and methanol in diesel engines, but there is a pressing need to further reduce engine emissions. To this end, a dual-fuel engine test bench was built based on a high-pressure common rail diesel engine with a methanol injection system at the intake manifold combined with a two-stage in-cylinder direct injection (pre-injection + main injection) F-T diesel. The combined effects of methanol substitution ratio (MSR), exhaust gas recirculation (EGR) and diesel oxidation catalyst (DOC) on the combustion and emission characteristics of the dual-fuel engine was investigated at 2000 rpm and 75 % load. The results show that EGR improves the combustion characteristics of the F-T diesel/methanol dual-fuel engine while adding a DOC significantly reduces engine gaseous emissions. However, as the MSR and EGR rate increase, NOx emissions decrease, but other emissions increase. NOx emissions were reduced by 73 % compared to the original engine emissions for an MSR of 30 % and an EGR rate of 15 % without a DOC. When the MSR is 0 %, the DOC promotes the conversion of NO to NO2. While, when the MSR greater than 0, the DOC promotes the conversion of NO2 to NO. When equipped with a DOC, CO, NO, NO2, NOx, MeOH, and HCHO emissions decrease as the EGR rate increases, with the reduction of CO and MeOH emissions being greater than 99.5 % and 93 %, respectively, and the maximum conversion efficiency for HCHO emissions being 82 %. The present study showcases the key challenges as well as advantages in the use of EGR combined with a DOC assisting the application of coal-based alternative fuels in dual-fuel engines.

Investigation on the effects of blending hydrogen-rich gas in the spark-ignition engine

In order to improve the energy efficiency of the internal combustion engine and replace fossil fuel with alternative fuels, a concept of the methanol-syngas engine was proposed and the prototype was developed. Gasoline and dissociated methanol gas (GDM) were used as dual fuels and the engine performance was investigated by simulation and experiments. Dissociated methanol gas is produced by recycling the exhaust heat. The performance and combustion process was studied and compared with the gasoline engine counterpart. There is 1.9% energy efficiency improvement and 5.5% fuel consumption reduction under 2000r/min, 100 N ⋅ m working condition with methanol substitution ratio of 10%. In addition, the engine efficiency further improves with an increase of dissociated methanol gas substitution ratio because of the increased heating value of the fuel and effects of hydrogen. The peak pressure in the cylinder and the peak heat release rate of the GDM engine are higher than that of the original gasoline engine, with a phase closer to the top dead center (TDC). Therefore, blending hydrogen-rich gas in the spark-ignition engine can recycle the exhaust heat and improve the thermal efficiency of the engine.

The effect of diesel pilot injection strategy on combustion and emission characteristic of diesel/methanol dual fuel engine

The effects of diesel fuel pilot injection timing, pilot mass percent and methanol substitution rate on the combustion and emissions of a diesel-methanol dual fuel engine were experimentally investigated. The experiments were conducted on a single-cylinder, naturally aspirated common rail diesel engine modified with a methanol injection system. The results indicated that the addition of pilot injection advanced the ignition time and increased the heat release rate. With the advancement of pilot injection timing, the ignition delay increased, and the indicated thermal efficiency reduced. The NOx emission first decreased and then increased while the smoke emission showed the opposite trend. With the increase in the pilot mass percent, the peak in-cylinder pressure and the heat release rate increased. Meanwhile, the ignition time and the CA50 advanced. At different pilot injection timing, the combustion duration and the indicated thermal efficiency showed different trends. Meanwhile, with the increase in the pilot mass percent, the NOx emission increased and the smoke emission decreased. When the MSR increases from 20% to 40%, the indicated thermal efficiency increases by 1.9 percentage points, and the NOx and smoke emissions decrease by 88% and 61% respectively by advancing the PIT and increasing the pilot mass percent with the EGR combined. It can be concluded that, at high MSR, advancing the pilot injection timing and increasing the pilot mass percent with EGR combined is a better injection strategy to improve the performance of combustion and emissions.

Experimental Study of Cyclic Variations of RCCI Diesel–Methanol Engines at Multiple Simulated Elevations

Abstract The cyclic variations of reactivity-controlled compression ignition (RCCI) combustion are studied in this work via experiments conducted in an in-house diesel–methanol dual-fuel (DMDF) engine at multiple simulated elevations. The test engine is maintained at 1800 rpm, with simulated elevations of 10, 700, and 1670 m. Engine load, methanol substitution rate (MSR), and injection parameters are varied to investigate their effects on cyclic variations at multiple elevations. We employ in-cylinder pressure parameters, such as the maximum pressure (Pmax) and indicated mean effective pressure (IMEP), to quantify cyclic variations. According to the results, the stability of DMDF combustion in plateau conditions displays a similar trend to that in plain conditions. However, with the increase in elevation, there is a significant increase in the Pmax coefficient of variation (COVPmax), while that of the IMEP (COVIMEP) shows an opposite trend. The distribution of crank angle at high elevations corresponding to Pmax tends to be more concentrated, and the increase in pilot injections reduces the COVPmax in the plateau environment. At all elevations, there is no effect of injection timing on COVIMEP, while COVPmax is more sensitive to injection timing (range from 10 deg CA before top dead center (BTDC) to 3 deg CA BTDC). Compared with other injection parameters, the cyclic variations caused by injection pressure (range from 92 MPa to 112 MPa) are relatively minor.

Effects of blending dissociated methanol gas with the fuel in gasoline engine

To improve the thermal efficiency and reduce the emissions of an internal combustion engine, this research proposed a new gasoline-syngas engine that used gasoline and dissociated methanol gas as the fuel. The system used exhaust heat to dissociate methanol into syngas, which was then added in an engine cylinder and blended with gasoline for combustion. The experimental data of the gasoline-syngas engine were compared with those of the original gasoline engine before the transformation. For a methanol substitution ratio of 20%, the equivalent fuel consumption rate, CO emission, and HC emission decreased by 4.3%, 37.8%, and 32.4%, respectively, and the NOx emission increased by 10.8% at a speed of 2000 r/min, torque of 60 N·m, and excess air ratio of 1. The NOx emission could be reduced by 72.2% by increasing the excess air ratio from 1 to 1.3. Blending the dissociated methanol gas with the fuel of the gasoline engine recycled the exhaust heat and changed the combustion characteristics of the fuel. It has broad application prospects for the efficient use of energy and reduction of emissions.

Study on the performance of diesel-methanol diffusion combustion with dual-direct injection system on a high-speed light-duty engine

To investigate the high methanol substitution ratio (MSR) combustion performance of diesel-methanol diffusion combustion (DMDC) mode, the engine experiments were conducted based on a high-speed light-duty engine with a dual-direct injection system in this study. Effects of MSR on the combustion, emission and energy distribution characteristics, as well as the difference between the DMDC mode and the conventional diesel combustion (CDC) mode, were investigated in detail under four engine loads at a constant engine speed of 3000 rpm and a similar CA50 of 7.5 °CA ATDC. The experimental results show that the MSR can reach 87% at BMEP = 0.55 MPa. Under all operating conditions, the NOx and soot emissions of the DMDC mode are significantly reduced simultaneously compared to those of the CDC mode, and the reduction is enlarged as both MSR and loads increase. At BMEP = 0.14 MPa, the indicated thermal efficiency (ITE), THC and CO emissions of the DMDC mode are inferior to that of the CDC mode. However, the combustion and emission performances are gradually improved when the BMEP exceeds 0.27 MPa. Especially at BMEP = 0.55 MPa, the THC and CO emissions of the DMDC mode are lower and the ITE increases by 10% compared to the CDC mode, and the ITE is more sensitive to the MSR. According to the energy distribution analysis, it can be found that the heat transfer loss and exhaust loss of the DMDC mode have been dramatically reduced, resulting in the increased ITE compared to the CDC mode.

Effect on the performance and emissions of methanol/diesel dual-fuel engine with different methanol injection positions

In methanol/diesel combined injection mode engines, the high latent heat of vaporization of methanol reduces the combustion temperature. It effectively reduced NOx emissions, which led to the deterioration of combustion under high blending ratio conditions. This study attempted to improve the adverse effect of high latent heat vaporization on combustion by changing the methanol injection positions. The experiment was carried out on a Yunnei D30 inline 4-cylinder turbocharged and intercooled common rail diesel engine. Methanol that used five kinds of methanol substitution rates (0%, 10%, 20%, 30%, 40%) was injected at three positions, namely pre-intercooler, post-intercooler, and intake manifold under three load conditions (100 N.m, 200 N.m, 300 N.m) with four engine speeds of 1200 rpm, 1400 rpm, 1800 rpm and 2000 rpm, respectively. The results showed that under medium and low load conditions, regardless of the injection position, the methanol substitution rate increased, the maximum explosion pressure in the cylinder decreased, the peak heat release rate shifted backward, the ignition delay prolonged, and total energy consumption increased, HC and CO emissions increased, and NOx emissions reduced. Under high load conditions, with the methanol substitution rate increasing, maximum explosion pressure first increased and then decreased. The total energy consumption first decreased and then increased, while the HC and CO emissions slightly increased and the NOx emissions decreased. Under medium and low load conditions, varying methanol injection positions could lessen the adverse effects of methanol blending combustion. Methanol injected into the pre-intercooler, which utilized the high temperature of intake air after pressurization, vaporized effectively, shortened ignition delay and combustion duration, and reduced HC and CO emissions. At post-intercooler, HC emissions slightly increased under low load conditions, ignition delay was shortened under medium load conditions, and cylinder pressure was restored to the level of pure diesel. Under high-speed and high-load conditions, due to higher cylinder temperature, HC and CO emissions decreased, and NOx emissions increased. At the intake manifold, the lowest in-cylinder pressure and slowest heat release rate were found at low-load conditions, but NOx emissions were reduced the most at high speed and high load conditions.