Direct-injection Spark-ignition Methanol Engine Research Articles

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.

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.

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.

Computational study of intake temperature effects on mixture formation, combustion and unregulated emissions of a DISI methanol engine during cold start

Direct injection spark ignition (DISI) methanol engines have an excellent lean-burn properties but with more unregulated emissions of formaldehyde and unburned methanol and cold start difficulties. In this study, intake temperature effects on mixture formation, combustion processes, and unregulated emissions of formaldehyde and unburned methanol were numerically simulated for a stratified-charge DISI methanol engine during cold start. Computational results show that increasing the intake temperature during cold start boosts the evaporation of methanol and improves the in-cylinder distribution of methanol-air mixture, thereby accelerating the combustion and mitigating formaldehyde and unburned methanol emissions. When the intake temperature increases from 283 K to 293 K, the ignition delay is reduced by 1.3°CA (crank angle). Meanwhile, the maximum cylinder pressure, maximum heat release rate, and maximum cylinder temperature increase by approximately 0.59 MPa, 20 J/°CA and 165 K, respectively; formaldehyde and unburned methanol emissions are reduced by 27% and 48%. When the intake temperature is further increased to 313 K, the effects on the engine operations as well as emissions become weaker. There were almost no improvements on combustion or unregulated emissions when the intake temperature was above 313 K.

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.

Numerical analysis of carbon monoxide, formaldehyde and unburned methanol emissions with ozone addition from a direct-injection spark-ignition methanol engine

Numerical simulations were performed to assess the relationship between carbon monoxide (CO) and formaldehyde and unburned methanol-unregulated emissions in cylinders and a tailpipe with ozone (O3) addition from a direct-injection spark-ignition methanol engine. This simulation study was performed during cold-start and steady-state modes with O3 addition of 3000 and 7000 ppm. The initial phase of produced CO and formaldehyde is advanced significantly with O3 addition, but the initial phase of produced unburned methanol had little impact. The effects of O3 addition on the formation and oxidation of CO, formaldehyde and unburned methanol are lower for the steady-state compared with the cold-start mode. The effects of O3 addition on CO, formaldehyde and unburned methanol production and consumption in the cylinder are formaldehyde > CO > unburned methanol. CO, formaldehyde and unburned methanol emissions decrease with increasing O3 addition. When the exhaust valve opened, CO, formaldehyde and unburned methanol emissions with 7000 ppm O3 addition for the cold-start mode are 15.3%, 52% and 70% lower than those without O3 addition, respectively. CO, formaldehyde and unburned methanol emissions with 7000 ppm O3 addition for the steady-state mode are 52.6%, 28% and 28% lower than those without O3 addition, respectively.

Numerical study of effect of injection and ignition timings on combustion and unregulated emissions of DISI methanol engine during cold start

Numerical simulations were performed for the effect of injection and ignition timings on combustion and the generation of formaldehyde and unburned methanol emissions in the cylinder of a stratified charge direct injection spark ignition (DISI) methanol engine during cold start using AVL-fire, coupling the methanol chemical and kinetic reaction mechanisms. A non-uniform spray-line distribution nozzle was used to form stratified charge methanol-air mixtures during cold start. The simulation shows that injection and ignition timings have a significant effect on the concentration distribution of the methanol-air mixture, and hence the affect combustion and generation of formaldehyde and unburned methanol emissions. Optimized injection and ignition timings form an ideal stratified charge distribution. Formaldehyde and unburned methanol emissions decrease with retarding of the injection timing, but increase with retarding of the ignition timing. Formaldehyde and unburned methanol emissions at injection timing 41°crank angle before top dead center (CABTDC) were 48% and 82% higher than for 57°CABTDC, and those at ignition timing 8°CABTDC were 125% and 900% higher than for 20°CABTDC, respectively. Optimal injection and ignition timings provide the best compromise between the maximum cylinder pressure, maximum heat release rate, maximum cylinder temperature, and formaldehyde and unburned methanol emissions. Injection timing 45°CABTDC and ignition timing 14°CABTDC obtained the best compromise on cold start performance.

Numerical study on combustion and emission in a DISI methanol engine with hydrogen addition

Combustion, carbon monoxide (CO), Nitrous oxide (NO), formaldehyde (HCHO) and unburned methanol (CH3OH) emissions characteristics in a direct injection spark ignition (DISI) methanol engine with hydrogen addition ratio from 5% to 15% have been investigated numerically based on the detailed methanol oxidation reaction mechanism combined with the nitrogen oxides (NOX) reaction mechanism using the PREMIX code of CHEMKIN program with AVL FIRE software. Maximum cylinder pressure, maximum heat release rate and highest cylinder temperature increase and their corresponding crank angles advance with hydrogen addition from 0 to 15%. CO emission decreases and NO emission increases with increasing hydrogen addition ratio, whereas, formaldehyde and the unburned methanol significantly reduce with increasing hydrogen addition. Thus, hydrogen addition can provide a new way to address formaldehyde and unburned methanol unregulated emissions in a DISI methanol engine.

Regulated and unregulated emissions from a DISI methanol engine under homogenous combustion and light load

Abstract Experiments were conducted on a four-cylinder direct-injection spark-ignition (DISI) methanol engine under homogenous combustion mode and light load. The measurement methods in which combine with gas chromatography and liquid chromatography were used to separate and measure formaldehyde (HCHO) and unburned methanol unregulated emissions. The effects of methanol injection timing, ignition timing, excess air ratio and intake air temperature on HC, CO, and NO X regulated emissions, HCHO and unburned methanol unregulated emissions, and brake thermal efficiency were investigated experimentally. The study results show that advancing methanol injection timing, HC and CO emissions decrease, and NO X emission increases. Retarding ignition timing, HC and NO X emissions decrease, the effect of ignition timing on CO emission is small. The HC, CO, and NO X emissions of rich mixture are higher than those of lean mixture. For a lean mixture, HC emission rises. The HC and CO emissions decrease as intake air temperature increases. Intake air temperature of 55 °C is suitable for making an ideal mixture for a DISI methanol engine under homogenous combustion mode. The variations in emitted HCHO and unburned methanol show an opposite tendencies with the variations in the methanol injection timing, ignition timing, excess air ratio, intake air temperature and engine speed. Retarding methanol injection timing, advancing ignition timing, using lean mixture and reducing intake air temperature can decrease HCHO emission; and vice versa, unburned methanol emission decrease.

Regulated emissions from a direct-injection spark-ignition methanol engine

The effects of injection timing, ignition timing, and injection nozzle parameters on the regulated emissions from a high-compression ratio direct-injection spark-ignition methanol engine were investigated experimentally and its emission characteristics were compared with the diesel counterpart. The experimental results indicated that the injection and ignition timings affect exhaust emissions significantly. Best compromises between the brake thermal efficiency and three emission pollutants at the optimal injection and ignition timings were obtained. The effects of injection nozzle parameters on emissions of methanol engine are significant. The THC (total hydrocarbon compounds) emission using an injector of a 10-hole × 0.30 mm nozzle is lower significantly than those of 7-hole × 0.45 mm nozzle in the overall load range and CO (carbon monoxide) emission is also lower, but NO x (nitrogen oxides) emission is higher at high load. The methanol engine is characterized by smokeless combustion. According to the ECE R49-13 mode test procedure, the brake specific NO x emission from the methanol engine is only nearly half that from the diesel counterpart and 11% lower for the CO emission, but 273% higher for the THC emission.

Experimental Study on the Stratified and Homogeneous Charge of a Direct-Injection Spark Ignition Methanol Engine

Based on the gasoline direct-injection spark ignition (DISI) engine technologies and methanol fuel characteristics, a complex-guided multi-hole spray coupled with induction swirl and chamber-wall-guided stratified-charge combustion system for a DISI methanol engine was developed. It was retrofitted from a four-cylinder diesel engine with a compression ratio of 14. It was developed to run on methanol in stratified-charge and homogeneous-charge combustion modes; under part-load operating conditions, stratified-charge combustion is adopted to improve fuel economy while, under high- and full-load conditions, the homogeneous-charge combustion mode is adopted for the purpose of a higher power output. Under both combustion modes, the key parameters of the combustion system were matched and optimized respectively. The operating map for both combustion modes was obtained. Then, the engine power performance, emissions, and combustion characteristics were studied. The power output of the developed methanol engine is higher than that of the original diesel engine. By using the stratified combustion mode under low-load conditions, the engine fuel economy (the brake thermal efficiency) is improved; the stratified-charge combustion of methanol performed relatively well with acceptable values of the coefficient of the cyclic variation in the indicated mean effective pressure. The smoke and nitrogen oxide emissions from the DISI methanol engine are both reduced simultaneously and significantly.

Improvement of fuel economy of a direct-injection spark-ignition methanol engine under light loads

The effects of ignition system, compression ratio, and methanol injector configuration on the brake thermal efficiency (BTE) and combustion of a high-compression direct-injection spark-ignition methanol engine under light loads were investigated experimentally, and its BTE was compared with its diesel counterpart. The experimental results showed that these factors significantly affect the fuel economy under light load. The BTE of a methanol engine using a high-energy multi-spark-ignition system is on average 25% higher than that of one using a single-spark-ignition system at a brake mean effective pressures (BMEP) of 0.11–0.29 MPa and an engine speed of 1600 rpm. Decreasing the compression ratio of the methanol engine from 16:1 to 14:1 markedly increases the BTE under low loads and decreases the BTE at high loads. For the methanol engine, using an injector of a 10-hole × 0.30 mm nozzle decreases the ignition delay and improves the fuel economy compared to when an injector of a 7-hole × 0.45 mm nozzle is used. The combustion duration using an injector of a 7-hole × 0.45 mm nozzle is much longer than that with one of a 10-hole × 0.30 mm nozzle under light loads. As a result, the BTE for a methanol engine with optimal parameters is improved by 27% compared to that for a methanol engine without optimized parameters at a BMEP of 0.17 MPa and an engine speed of 1600 rpm, but the BTE of the optimized methanol engine is 20% lower than that of its diesel counterpart under these operating conditions.

Effect of injection and ignition timings on performance and emissions from a spark-ignition engine fueled with methanol

Optimal injection and ignition timings and the effects of injection and ignition timings on performance and emissions from a high-compression direct-injection stratified charge spark-ignition methanol engine have been investigated experimentally. The results have shown that direct-injection spark-ignition methanol engine, in which a non-uniform mixture with a stratified distribution can be formed, has optimal injection and ignition timings to obtain a good combustion and low exhaust emissions in the overall mode range. Both methanol injection timing and ignition timing have a significant effect on methanol engine performance, combustion, and exhaust emissions. At an engine speed of 1600 rpm, full load, and optimal injection and ignition timings, methanol engine can obtain shorter ignition delay, lesser cycle-by-cycle variation, the maximum in-cylinder pressure, the maximum heat release rate, and higher thermal efficiency compared to the case of non-optimized injection and ignition timings. For methanol engine, the optimization of injection timing and ignition timing can lead to an improvement of brake-specific fuel consumption of more than 10% compared to non-optimized case in the overall load range and engine speed of 1600 rpm. The best compromise between thermal efficiency and exhaust emissions is reached at optimal injection and ignition timings.