Spark-ignition Methanol Engine Research Articles

Simulation Analysis of a Methanol Fueled Marine Engine for the Ship Decarbonization Assessment

Methanol as marine fuel represents one of the most cost-effective and practical solutions towards low-carbon shipping. Methanol fueled internal combustion engines have a high level of technological readiness and are already available on the market; however, technical data in terms of fuel consumption and emissions are not yet easily accessible. For this reason, the present study deals with the simulation of a virtual spark-ignition methanol engine, carried out in a Matlab-Simulink© R2023a environment to assess the CO2 emissions in several working conditions of a possible ship power system. The thermodynamic model of the methanol fueled engine is derived from a marine gas engine simulator, already validated by the authors in a previous work. This article presents the relevant modifications necessary to adapt the engine to the methanol fuel mode with regard to the different fuel characteristics. The simulation analysis compares the results of the virtual methanol engine with available data from a similar, existing gas engine, highlighting the differences in efficiency and carbon dioxide emissions.

Experimental study on the emission characteristic of a methanol engine based on transient cycle WHTC

The emission characteristics of regulated emissions and unregulated emissions were studied under the full loads and the cold/hot transient cycle (WHTC) on a six-cylinder, multi-point injection, and spark ignition methanol engine. The results show that the emissions of THC and CO for the methanol engine is at a high level without three-way catalyst (TWC) and the emission of NOX could be controlled at a lower level than 400 mg/kW·h with exhaust gas recirculation (EGR). The emissions of THC, CO and NOX are low with TWC, whose weighted results under WHTC could be kept at a lower level than the limits in China VI Standard. It is a technical difficulty to control the emissions of methanol (CH3OH) and formaldehyde (HCHO) for methanol engines, especially under the cold WHTC, there has a high risk for the emission of CH3OH exceeding the limit of standard.

Computational study of added H2 impacts on mixture formation, OH radical and unregulated emissions of spark-ignition methanol engine under various boundary parameters

Numerical simulations of hydrogen (H2) impacts on mixture formation, OH radical generation, and formaldehyde (HCHO) and unburned methanol (CH3OH) emissions of spark-ignition (SI) methanol engine based methanol late-injection strategy under different methanol injection timings (MIT), ignition timings (IT), excess air ratios (λ) and added H2 ratios (RH2) boundary parameters were conducted. The simulation results show that the ideal methanol concentration distribution is obtained at the MIT = 85°CA BTDC. The OH radical plays a dominant role in methanol oxidation. The OHPMF (peak OH radical mass fraction) of RH2 = 9 % ≫ OHPMF of RH2 = 6 % > OHPMF of RH2 = 3 % > OHPMF of RH2 = 0 % at MIT = 85°CA BTDC. Compared with IT and λ, the RH2 is more decisive for the generation of OH radical. The HCHO is a major intermediate and an important unregulated emission of methanol engine. In the initial stage of methanol reaction, added H2 can accelerate the generation of OH radical, further promote the oxidation of methanol, and greatly raise the generation of HCHO. The peak HCHO mass fraction increases with the increase of RH2. At MIT = 85°CA BTDC and exhaust valve opening, the HCHO emission of RH2 = 3 %, 6 %, and 9 % is approximately 51 %, 76.5 % and 89.4 % lower than that of RH2 = 0 %, respectively. The generation and post-oxidation of HCHO mainly depended on average in-cylinder temperature. There is a lowest CH3OH emission at MIT = 85°CA BTDC, IT = 28°CA BTDC, λ = 1.4 and pure methanol. At MIT = 85°CA BTDC, λ = 1.4 and exhaust valve opening, the CH3OH emission of RH2 = 3 %, 6 %, and 9 % is approximately 52.8 %, 75.5 % and 92.5 % lower than that of RH2 = 0 %, respectively.

Numerical investigations on the effects of EGR routes on the combustion characteristics and efficiency of a heavy-duty SI methanol engine

Exhaust gas recirculation (EGR) is one effective strategy to improve the thermal efficiency of the heavy-duty spark-ignition (SI) methanol engine. The high EGR tolerance of methanol engine raises new requirements for the EGR system. In this study, the influences of three different EGR routes, high-pressure EGR (HP-EGR), low-pressure EGR (LP-EGR), and high-low-pressure EGR (HLP-EGR) on the engine performance were studied by the one-dimensional simulation with the predictive combustion sub-model. The investigation was conducted at 1000 rpm and 1400 rpm, and 50% and 100% full load. Results show that EGR routes influence both the combustion characteristics and pumping mean effective pressure (PMEP), thus affecting the brake specific fuel consumption (BSFC). The EGR route with the lower internal EGR rate has a lower in-cylinder temperature at the compression stroke, a weaker knock tendency and a more advanced combustion phase. The effects of EGR routes on BSFC are more significant at the higher engine speed. The optimal BSFC of HP-EGR is lower than that of HLP-EGR and LP-EGR by up to 16.4 g/k·Wh and 21.2 g/k·Wh. Considering the engine performance at all engine operating conditions, HP-EGR is the optimal EGR route while LP-EGR is the worst one for the heavy-duty SI methanol engine.

Numerical study of the firing, radicals and intermediates in the combustion process of a H2-assisted combustion DISI methanol engine

The firing, radicals and intermediates in the combustion process of a port-injection hydrogen (H2)-assisted combustion direct-injection spark-ignition (DISI) methanol engine were numerically simulated. The engine with port-injection H2 plus direct-injection methanol was tested at 1800 rpm with intake manifold absolute pressure of 68 kPa. AVL-Fire coupling the detailed methanol chemical kinetics modeling with 21 components and 84 elementary reactions was used to simulate in this study. The model calculation results agreed well with the experiments, and the average error is less than 3% and can guarantee other outcomes. The simulation results show that high added H2 ratio (RH2) has higher turbulent kinetic energy in the region closer to the combustion chamber wall. When RH2 is greater than 6%, the formation time of fire core is obviously shortened and the average flame propagation velocity is significantly increased. Increasing RH2, the generation speed and the peak value of H, O and OH radicals increase, and higher concentration of radicals accelerates the diffusion of combustion from the hot flame zone. OH radical is a key reactant, which always plays a decisive role in the process of methanol oxidation. Effect of added H2 on methanol oxidation reaction is reflected in accelerating the initial stage of combustion and ameliorating the intensity of reaction. The mass fractions of HCHO, HCO and CO, as the main intermediate products, all show a trend of increasing first and then decreasing with the crank angle (CA), and their peak values indicate the phase of the most violent reaction. The peak values of HCHO and HCO are all near the top dead center (TDC), which is consistent with the trend of H and OH radicals generation rate. The relationship between consumption rate of methanol and CA shows that the consumption rate of methanol at RH2 = 9% is the earliest and steepest, and most of methanol has been consumed by reaction before TDC. Added H2 accelerates the fire propagation, H2 dominates the process of radical formation and methanol chain reaction, the flame spread period is shortened rapidly, and the effect of added H2 to promote combustion is obvious.

Investigation on injection strategy affecting the mixture formation and combustion of a heavy-duty spark-ignition methanol engine

Methanol is thought as a carbon neutral fuel and one of the most promising alternative fuels for spark-ignition (SI) engine. On the basic combustion theory of SI engines, mixture formation plays an important role in the SI engine performance. However, there is a lack of investigation on the mixture formation process of heavy-duty (HD) port fuel injection (PFI) SI methanol engines. Therefore, experiments and simulations were conducted on a HD PFI SI engine fueled with pure methanol. The effects of the injection timing (αinj) on the mixture formation process, combustion and emission characteristics were investigated. Methanol engine performance can be predicted by the mixture homogeneity which is deeply affected by injection timing. When αinj was 240°CA, 360°CA and 480°CA, there were three typical mixture formation modes, namely “spray”, “premix and spray” and “premix” mode, respectively. The mixture homogeneity increased first and then decreased while the in-cylinder temperature at the spark timing increased monotonically as αinj varied from 240°CA to 480°CA at the interval of 120°CA. The “premix and spray” mode was the optimal mixture formation strategy from the perspective of promoting mixture homogeneity and decreasing the in-cylinder mixture temperature. When αinj was from 120°CA to 300°CA, the leaner mixture around the spark plug and lower mixture prolonged or retarded CA0-10, CA10-90 and CA50. The above combustion characteristics contributed to a lower engine brake thermal efficiency (BTE) at αinj of 120°CA to 300°CA. As αinj varied from 0°CA to 720°CA, HC emissions increased first and then decreased while CO emissions did the opposite. Both HC and CO emissions at αinj of 360°CA were at low levels. The more HC emission was caused by the more regions with the richer mixture in the crevice formed by the piston and liner. The CO emission was determined by the volume of regions with the richer mixture in the combustion chamber and in-cylinder mixture temperature. The “premix and spray” mode should be adopted to improve the BTE and reduce both HC and CO emissions.

Cylinder-to-cylinder variation of knock and effects of mixture formation on knock tendency for a heavy-duty spark ignition methanol engine

The knock characteristics of a high-pressure port fuel injection heavy-duty SI engine fueled with pure methanol were investigated experimentally and numerically. This paper aims to provide the optimization direction of the injection strategy from the perspective of knock suppression and thermal efficiency improvement. Both experiment and simulation prove that injection during the intake stroke with high injection pressure can mitigate knock because the strong interaction between spray and intake flow helps to form the more homogeneous and lower temperature mixture which prolongs the ignition delay of end-gas. As the injection timing (αinj) varies from 320°CA to 480°CA, the combustion speed and thermal efficiency increase first and then decrease, while the knock tendency is the opposite. Take the combustion at αinj of 320°CA as a baseline, the faster combustion speed at αinj of 380°CA caused by the homogeneous mixture contributes to the higher thermal efficiency, while that of 480°CA caused by the higher temperature further enhances the knock tendency. There is a significant cylinder-to-cylinder variation of the knock tendency. The knock tendency of the cylinder with the less fresh air charge is lower because of the lower in-cylinder temperature and pressure.

Investigation on mixture formation and combustion characteristics of a heavy-duty SI methanol engine

• A high-pressure PFI system is utilized on a heavy-duty methanol SI engine. • The mixture formation process and its homogeneity are studied theoretically. • The optimized injection strategy can improve the mixture homogeneity. • The optimized injection strategy can improve the engine brake thermal efficiency. Due to the simplicity of the exhaust gas aftertreatment system, the heavy-duty natural gas spark ignition (SI) engines play an important role in achieving the macro targets of the reduction of petroleum consumption, carbon and harmful emissions. Considering that power-to-methanol is economically more feasible than power-to-methane, methanol is proposed to continue the advantages of natural gas engines. Based on the fuel properties of methanol and our researching experience, methanol mixture preparation and flow within the cylinder are the most significant. A novel high-pressure port fuel injection (PFI) system is utilized to promote atomization and evaporation of methanol. The effects of the injection strategy, including injection pressure (p inj ) and injection timing (α inj ), and excess air–fuel ratio (λ) on the mixture formation were simulated and then studied by engine experiments. Three-dimensional simulation and engine tests were conducted under the condition of 1500 rpm and the brake mean effective pressure (BMEP) of 0.854 MPa. p inj varied from 8 MPa to 24 MPa by 4 MPa, α inj was from 240°CA BTDC to 400°CA BTDC by 40°CA and λ was set to be 1.1,1.2 and 1.3, respectively. Simulation results indicate that the mixture homogeneity can be promoted by the optimized injection strategy. The mixture is the most homogeneous at α inj = 340 °CA BTDC and p inj = 8 MPa and the most inhomogeneous at α inj = 400 °CA BTDC and p inj = 24 MPa when λ = 1.2. The experimental results indicate that the more homogeneous mixture can improve engine brake thermal efficiency by shortening CA 0-10 and CA 10-90 as well as methanol lean-burn. The optimized injection strategy can improve the brake thermal efficiency by 2.6%, 2.7% and 2.8% when λ = 1.1, 1.2 and 1.3, respectively.

Numerical study of cold-start performances of a medium compression ratio direct-injection twin-spark plug synchronous ignition engine fueled with methanol

The cold-start mixture preparation, combustion and emissions behaviors of a medium compression ratio direct-injection twin-spark plug synchronous ignition engine fueled with methanol were numerically simulated. Simulation results display that the methanol injection timing, ignition timing and the global equivalence ratio had an important influence on the concentration distribution of methanol-air mixture, the flow velocity, and the density of the flame surface during cold start. Ignition delay period reached the shortest at injection timing 70°CA BTDC. Ignition delay period for injection timing 130°CA BTDC and 50°CA BTDC increased 209% and 45.5% compared to injection timing 70°CA BTDC, respectively. Ignition delay period reached the shortest at ignition timing 21°CA BTDC. Ignition delay period of twin-spark plug was shorter than that of single-spark plug at the same equivalence ratio. There existed the maximum in-cylinder pressure, maximum heat release rate, maximum in-cylinder temperature, lowest unburned methanol and soot emissions, and highest NOX emissions at injection timing 70°CA BTDC. The maximum in-cylinder pressure, maximum heat release rate, and maximum in-cylinder temperature gradually increased with the advance of ignition timing. Injection timing 70°CA BTDC, ignition timing 21°CA BTDC, and equivalence ratio 0.9 could obtain the best cold start performance compromise using twin-spark plug ignition mode. At equivalence ratio 1.0, twin-spark plug ignition had better combustion performances, lower unburned methanol and soot emissions, and higher NOX emissions compared with single-spark plug ignition. Twin-spark plug synchronous ignition had more advantageous to cold starting ignition compared with single-spark plug ignition for a medium compression ratio direct-injection spark-ignition methanol engine.

Optimization on timings of injection and spark of a high compression-ratio stratified-charge methanol engine under ultra-lean burn

High compression-ratio and ultra-lean burn are the two most effective measures to enhance economy of spark-ignition engines. The investigations were performed on a high compression-ratio stratified-charge direct-injection spark-ignition methanol engine with an injector of non-uniform spray-line distribution. The effect of timings of injection and spark on the concentration field of the stratified-charge mixture, combustion and emissions behaviors of methanol engine under ultra-lean burn conditions was studied by simulation. Simulation results demonstrated that an ideal stratified-charge mixture was the guarantee to obtain the best performance of a high compression-ratio spark-ignition methanol engine under ultra-lean burn. The timings of injection and spark had a remarkable effects on mixture formation, combustion and emission of a methanol engine under ultra-lean burn. There existed an optimal timings of injection and spark to obtain the peak in-cylinder pressure, peak heat release rate and peak in-cylinder temperature of methanol engine under ultra-lean burn, as well as the shortest ignition delay and combustion duration. Lower CO (carbon monoxide), unburned methanol and soot emissions, and higher NO (nitric oxide) emission were acquired at optimal timings of injection and spark under high compression-ratio and ultra-lean burn. Hence, realizing an ideal stratified-charge combustion was the key to obtain the best performance of a spark-ignition methanol engine under high compression-ratio and ultra-lean burn.

Evaluation on combustion and lean-burn limit of a medium compression ratio hydrogen/methanol dual-injection spark-ignition engine under methanol late-injection

Lean-burn is an effective way to optimize the fuel economy of spark-ignition methanol engines. Hydrogen-assisted combustion can improve the stability of combustion and increase the lean-burn limit of such engines. In this study, a medium compression ratio of port injection-type hydrogen/direct-injection methanol was used in a dual-injection spark-ignition engine to investigate the combustion and lean-burn limit under different ratios of addition of hydrogen, excess air ratios, and ignition timings based on methanol late-injection. The results show that the timing of ignition of the hydrogen-enriched methanol engine could be retarded without worsening combustion to a greater extent compared with that in the methanol engine. The timing of ignition had little effect on the coefficient of variation of the indicated mean effective pressure after the addition of hydrogen under lean-burn conditions. Its addition increased the lean-burn limit. The greater the amount of hydrogen added was, the higher the lean-burn limit was. The influence of excess air ratio on the parameters of combustion for 9% of added hydrogen was much smaller than that without hydrogen addition. The critical hydrogen addition ratio from “hydrogen-assisted combustion” to “dual-fuel combustion” was 6%.The optimal ignition timing corresponding to the lean-burn limit at different ratios of added hydrogen was in the range of 33°–42° of the crank angle before the top dead center. Thus, hydrogen-assisted combustion can significantly improve the stability of combustion and increase the lean-burn limit to an excess air ratio of approximately three in a direct-injection spark-ignition methanol engine with a medium compression ratio.

Experimental assessment of lean-burn characteristics for a modified diesel engine operated in methanol direct injection spark ignition (DISI) mode at full throttle condition

In this study,the lean-burn characteristics of a high-compression direct injection spark ignition (DISI) methanol engine were investigated. The tests were conducted on a modified diesel engine in methanol DISI mode at three excess air ratios (1.2, 1.3, and 1.4) and injection timings from −60° to −300° crank angle (CA) after top dead center (ATDC). The engine was run at 1500 rpm, 100% throttle opening, and spark timing at maximum brake torque condition. The results demonstrated that the test engine under lean-burn condition can obtain the higher indicated thermal efficiency (ITE), but the lower indicated mean effective pressure (IMEP). The THC, CO, CO2 and NOX emissions are all reduced with the increased λ. Injection timing had a large influence on the combustion and emissions and these influences became largely in the case of retarded injection conditions. There existed an optimum injection timing of −240 °CA ATDC where the IMEP and ITE got their highest values along with the lowest coefficient of variation in indicated mean effective pressure (COVIMEP). Meanwhile, the THC and CO emissions are lowest, but the CO2 and NOX emissions highest. The methanol engine can obtain the maximum toque of 27.6 N·m, which is 25.3% more than the original diesel engine at the same speed. Meanwhile, there was no knocking throughout the entire experiment, and the maximum pressure rise rate and COVIMEP were found to be 0.4 MPa and 4.1%, and those are much less than the critical points of 1.0 MPa and 5%, respectively.

Computational study of nozzle spray-line distribution effects on stratified mixture formation, combustion and emissions of a high compression ratio DISI methanol engine under lean-burn condition

In this paper, five different spray-line distribution nozzles were designed to evaluate the effect of the nozzle spray-line distribution on stratified-charge combustion of methanol engine. Nozzle spray-line distribution characteristics, the stratified mixture formation, combustion and emissions of a high compression ratio direct-injection spark-ignition methanol engine for different spray-line distribution nozzles under lean-burn condition were numerically simulated. Simulation results showed that a non-uniform spray-line distribution nozzle of a 10-hole × 0.30 mm was conducive to form an ideal stratified mixture and obtain better combustion and engine performance. The maximum in-cylinder pressure of nozzle A was approximately 50.5% higher than that of nozzle E. The ignition delay and combustion duration of nozzle A were approximately both 20% lower than nozzle E. Nozzle A had lower unburned methanol, CO and soot emissions. The nozzle order of the highest NO emission was: A ≫ B > C > D > E. NO emission of nozzle A was approximately 13.6 times higher than that of nozzle E. According to the combustion and emission performance tradeoff, the nozzle order was: A > B > D > C > E. Nozzle A was preferred for actual spark ignition methanol engine applications.

Assessment of ultra-lean burn characteristics for a stratified-charge direct-injection spark-ignition methanol engine under different high compression ratios

Lean burn is one of the most important characteristics of a stratified-charge direct-injection spark-ignition engine. In this study, a non-uniform 10-hole × 0.30 mm spray-line distribution nozzle was chosen to achieve stratified-charge of the methanol/air mixture. The mixture formation, combustion, and emissions characteristics of a stratified-charge direct-injection spark-ignition methanol engine under five global equivalence ratios and three high-compression ratios were simulated to assess its ultra-lean burn characteristics. The results showed that the equivalence ratio of the stratified-charge direct-injection spark-ignition methanol engine for stable combustion at high compression ratio was as low as 0.20. The ignition delay and combustion duration decreased as the compression ratio increased at high equivalence ratio, and vice versa at low equivalence ratio. The stratified-charge direct-injection spark-ignition methanol engine greatly reduced nitric oxide emissions under ultra-lean combustion. The unburned methanol, carbon monoxide, and soot emissions increased slowly as equivalence ratio decreased at all compression ratios and equivalence ratio >0.25. The indicated thermal efficiency decreased with decreasing compression ratio at high equivalence ratio, and vice versa at low equivalence ratio. For an equivalence ratio of 0.67, the indicated thermal efficiency at compression ratio of 14 was approximately 14.9% lower than at compression ratio of 16. However, for an equivalence ratio of 0.20, the indicated thermal efficiency at compression ratio of 14 was approximately 13.5% higher than at compression ratio of 16. The compression ratio of 14 was more favorable for the stratified-charge direct-injection spark-ignition methanol engine to achieve ultra-lean burn and find practical application.

Effects of the initial flame kernel radius and EGR rate on the performance, combustion and emission of high-compression spark-ignition methanol engine

As clean fuel, methanol is considered to be one of the most promising alternative to conventional fuels for internal combustion engines. In this paper, a four-cylinder ignited methanol engine simulation model was built by using a one-dimensional simulation software. The methanol engine was converted from a diesel engine with a compression ratio of 17.5, and the methanol injector was installed in the inlet. Setting the engine speed as 2400 r/min, the effects of the initial flame kernel radius and EGR rate on the performance, combustion and emissions of methanol engine were studied when the throttle opening was 10%, 30%, 50%, 70% and 90%, respectively. The results showed that at any throttle opening, with the increase of EGR rate, the performance of the engine decreased, the in-cylinder combustion deteriorated, the NOx emission decreased significantly, but the HC and CO emission increased. At any throttle opening, the engine performance decreased slightly with the increase of the initial flame kernel radius, and the combustion was optimized. In terms of emission, when the throttle opening was between 10% and 70%, the NOx and CO emission decreased with the increase of the initial flame kernel radius. When the throttle opening was 90%, the NOx and CO emission increased with the increase of the initial flame kernel radius.

Experimental Investigation of Diluents Components on Performance and Emissions of a High Compression Ratio Methanol SI Engine

Increasing compression ratio and using lean burn are two effective techniques for improving engine performance. Methanol has a wide range of sources and is a kind of suitable fuel for a high-compression ratio spark-ignition lean burn engine. Lean burn mainly has a dilution effect, thermal effect and chemical effect. To clarify the influences of different effects and provide guidance for improving composition of dilution gases and applications of this technology, this paper chose Ar, N2 and CO2 as diluents. A spark-ignition methanol engine modified from a diesel engine with a compression ratio of 17.5 was used for the experiments. The results obtained by using methanol spark ignition combustion indicated that at engine speed of 1400 rpm and 25% load, NOx dropped by up to 77.5%, 100% and 100% by Ar, CO2 and N2. Gases with higher specific heat ratio and lower heat capacity represented by Ar exhibited the least adverse effect on combustion and showed a downward break-specific fuel consumption (BSFC) trend. Gas with high specific heat capacity represented by CO2 can decrease NOx and total hydro carbons (THC) emissions at the same time, but the BSFC of CO2 showed the worst trend, followed by N2. Gas affecting the combustion process like CO2 had chemical effect.

Effect of injection strategy on cold start firing, combustion and emissions of a LPG/methanol dual-fuel spark-ignition engine

The spark ignition (SI) methanol engine is particularly difficult for cold start at low ambient temperature. Adding liquefied petroleum gas (LPG) can ensure a successful cold start of SI methanol engine. Based on a single-cycle fuel injection strategy, the effects of the amount and injection timings of methanol and LPG per cycle were experimentally investigated on cold start firing and emissions of a LPG/methanol dual-fuel SI engine. The results show that the minimum amount of LPG injected per cycle is the key factor to determine the reliable firing of LPG/methanol engines at low ambient temperatures. In order to form an ideal mixture in the firing cycle, 300 °CA injection interval between methanol and LPG is feasible to be used. Fuel injection parameters have great influences on the HC emissions, which are 74.4% lower under critical firing than that of misfiring mode. By altering injection parameters, unburned methanol shows opposite tendencies with formaldehyde emissions and similar tendencies with HC emissions.

Influence of ignition timing on combustion and emissions of a spark-ignition methanol engine with added hydrogen under lean-burn conditions

Ignition timing is an important parameter that impacts flame formation, early combustion process, and emissions of spark-ignition (SI) engines. Hydrogen as an auxiliary fuel may improve combustion and emission characteristics of SI engines. In this study, we experimentally investigated the effects of ignition timing on combustion and emissions of an SI methanol engine with added hydrogen at different engine speeds. At low engine speeds with various ignition timings, increasing hydrogen decreases indicated mean effective pressure, maximum cylinder pressure, maximum heat release rate, and combustion duration. While at high engine speeds with different ignition timings, more hydrogen increases the indicated mean effective pressure, maximum cylinder pressure, maximum heat release rate, and decreases the ignition delay, combustion duration, and COVimep. By comparison with cases without hydrogen, the COVimep can be respectively reduced by 21.5% and 36.8% with hydrogen ratios of 3% and 6% at engine speed of 2400 rpm and ignition timing of 28 °CABTDC. In addition, hydrogen additive decreases the carbon monoxide (CO) and hydrocarbon (HC) emissions at low engine speeds, but increases the nitrogen oxides and soot emissions at high engine speeds under various ignition timings.

Numerical study of plasma produced ozone assisted combustion in a direct injection spark ignition methanol engine

Numerical simulations were performed to better assess the effect of plasma produced ozone assisted combustion. The effects of ozone (O3) addition from 0 to 7000 ppm in the intake manifold on cylinder pressure history, ignition delay, cylinder temperature history, and formaldehyde unburned methanol emission of a direct injection spark ignition (DISI) methanol engine during cold start and steady state conditions were simulated using computational fluid dynamics to couple the methanol chemical and kinetics reaction mechanisms. The model results show that the maximum cylinder pressure increases with increasing O3 addition for cold start and steady state modes. O3 addition can also significantly reduce ignition delay. Two maximum heat release rate peaks occurred with O3 addition for cold start and steady state modes. The effect of O3 addition on combustion processes of DISI methanol engines was significantly greater for cold start than steady state mode, particularly with higher O3 concentrations. The effects on formation and oxidation of formaldehyde were greater than for unburned methanol, and the effects on formation and oxidation of formaldehyde were also significantly greater for cold start than steady state mode.

Detection and analysis of formaldehyde and unburned methanol emissions from a direct-injection spark-ignition methanol engine

A sampling system to collect exhaust emissions of a methanol engine by means of a sampling bag and an absorber was designed to absorb formaldehyde and unburned methanol emissions with deionized pure water. Three novel measurement methods that combine gas chromatography and liquid chromatography (GCLC), gas chromatography and the light spectrum (GCLS), and liquid chromatography and light spectrum (LCLS) were used to separate and measure formaldehyde and unburned methanol emissions. The three measurement methods of GCLC, GCLS and LCLS proved suitable and reliable to separate and measure the formaldehyde and unburned methanol emissions from a direct-injection spark-ignition methanol engine. The effects of methanol injection timing, spark timing, and excess air ratio on formaldehyde and unburned methanol emissions were analyzed experimentally by measurement method of GCLS. The formaldehyde and methanol detection limits are 0.16 μg/mL and 0.18 μg/mL for gas chromatography (GC), respectively, the detection limit for methanol is 0.15 μg/mL for liquid chromatography (LC), and the detection limit for formaldehyde is 0.21 μg/mL for light spectrum (LS). Retarding the spark timing increases the formaldehyde emission and decreases the unburned methanol emissions. The formaldehyde emission decreases rapidly and the unburned methanol emission increases significantly with an increasing excess air ratio.