Search

• H 2 -assisted combustion was proposed to improve the combustion process of methanol engine. • The role of H 2 -assisted combustion in DISI methanol engine was revealed. • Added H 2 accelerates the fire propagation, H 2 dominates the process of radical formation and methanol chain reaction. • The peak values of HCHO and HCO are all near the top dead center, which is consistent with the trend of H and OH radicals generation rate. • OH radical plays an important role in the process of methanol oxidation reaction. The firing, radicals and intermediates in the combustion process of a port-injection hydrogen (H 2)-assisted combustion direct-injection spark-ignition (DISI) methanol engine were numerically simulated. The engine with port-injection H 2 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 H 2 ratio (R H2) has higher turbulent kinetic energy in the region closer to the combustion chamber wall. When R H2 is greater than 6%, the formation time of fire core is obviously shortened and the average flame propagation velocity is significantly increased. Increasing R H2 , 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 H 2 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 R H2 = 9% is the earliest and steepest, and most of methanol has been consumed by reaction before TDC. Added H 2 accelerates the fire propagation, H 2 dominates the process of radical formation and methanol chain reaction, the flame spread period is shortened rapidly, and the effect of added H 2 to promote combustion is obvious. [ABSTRACT FROM AUTHOR]

• Dual-injection is used to improve particulate emission of GDI engine. • Combustion and emissions under different direct-injection ratios, throttle percentages and direct-injection timings are studied. • The role of dual-injection at low and medium loads is revealed. • For late direct-injection mode, soot emission increases rapidly with increasing direct-injection ratio. • Through comprehensive compromise of combustion and emission performance, the best direct-injection ratio is 40%–60%. Dual-injection in a spark-ignition engine has attracted extensive attention due to the advantage in controlling mixture formation and particulate emissions. The influence of direct-injection ratio (R DI) on combustion and emissions of a stoichiometric spark-ignition dual-injection gasoline engine at different throttle percentages (TP) and injection timings of direct-injection (DIIT) was investigated experimentally. Experimental results show that at a constant R DI (R DI > 0), the MCP (maximum cylinder pressure) TP=15%, DIIT=280°CA BTDC > MCP TP=15%, DIIT=50°CA BTDC ≫MCP TP=7%, DIIT=280°CA BTDC > MCP TP=7%, DIIT=50°CA BTDC. The R DI has a significant effect on low and medium loads and DIIT = 50°CA BTDC. The maximum cylinder pressure, maximum heat release rate and maximum cylinder temperature fall significantly with increasing R DI , and their corresponding crank angles are delayed obviously with increasing R DI. The R DI has an obvious influence on combustion starting point, combustion center and combustion duration at low load and late DIIT. At R DI = 100%, the COV imep (coefficient of variation in indicated mean effective pressure) of TP = 7% and DIIT = 50°CA BTDC reaches the highest value of 13%. Except TP = 7% and DIIT = 50°CA BTDC, the COV imep of other case conditions can be controlled below 5%. At R DI = 50%, BSNO X (brake-specific nitrogen oxides) TP=15%, DIIT=280°CA BTDC emissions are approximately 23.3%, 128.4% and 214.1% higher than BSNO X TP=7%, DIIT=280°CA BTDC , BSNO X TP=15%, DIIT=50°CA BTDC and BSNO X TP=15%, DIIT=280°CA BTDC emissions, respectively. At R DI = 50%, the soot TP=15%, DIIT=50°CA BTDC emission is approximately 49.9% higher than soot TP=7%, DIIT=50°CA BTDC emission, soot TP=7%, DIIT=50°CA BTDC emission is approximately 28.6 times higher than soot TP=15%, DIIT=280°CA BTDC emission, and soot TP=15%, DIIT=280°CA BTDC emission is approximately 11.1% higher than soot TP=7%, DIIT=280°CA BTDC emission. Through comprehensive compromise of combustion and emission performance, the best R DI is 40%–60%. [ABSTRACT FROM AUTHOR]

A non-uniform spray-line distribution nozzle was used to form a stratified charge distribution of methanol-air mixture in-cylinder. Computational fluid dynamics were employed to simulate the methanol chemical kinetics reaction mechanism. The effects of an overall methanol-air equivalence ratio on the mixture distribution of the in-cylinder, cylinder pressure, heat release rate, cylinder temperature, and unregulated formaldehyde and unburned methanol emissions of a stratified charge spark ignition direct injection methanol engines were investigated. The simulation agrees well with experimental results. The maximum cylinder pressure, maximum heat release rate, and maximum cylinder temperature, for an overall equivalence ratio of 0.67, are 65%, 172% and 51% higher than for 0.33, respectively. Formaldehyde and unburned methanol emissions for an overall equivalence ratio of 0.67 are 97% and 95% lower than for 0.33, respectively. Formaldehyde and unburned methanol are mainly from the region close to the cylinder wall. Larger cylinder temperatures produce faster oxidation and hence generate lower concentrations of formaldehyde and unburned methanol, and vice versa . When the maximum cylinder temperature exceeds 1500 K, formaldehyde and unburned methanol emissions are approximately 30 and 300 ppm, respectively. [ABSTRACT FROM AUTHOR]

• Combustion and emissions at stoichiometric and lean-burn conditions were studied. • Combustion mechanism of CO 2 and EGR dilution at half-load of GDI engine was revealed. • Deterioration combustion of CO 2 dilution was weaker than EGR dilution. • Dilution rate of CO 2 with the same combustion was much higher than that of EGR. In this paper, CO 2 or EGR (exhaust gas recirculation) as dilution gas was introduced into the intake system. The impacts of CO 2 or EGR dilution on combustion and emissions of a GDI (gasoline direct injection) engine at half-load, stoichiometric and lean-burn conditions were investigated experimental by comparison. The study findings show that the deterioration combustion of CO 2 dilution was weaker than that of EGR dilution. Dilution rate of CO 2 dilution for the same combustion process was about 2 times of EGR dilution. At 20% dilution rate, the combustion center for CO 2 dilution was roughly 25.2% and 13.9% earlier than that of EGR dilution at stoichiometric and lean-burn mixture, severally; the CO and HC emissions for CO 2 dilution were roughly 43.7% and 28.6% lower than those of EGR dilution at stoichiometric mixture, severally; and the NO X emissions for EGR dilution were around 74.8% and 58.7% lower than those of CO 2 dilution at stoichiometric and lean-burn mixture, severally; and the soot emission of CO 2 dilution was roughly 26.5% higher than that of EGR dilution at stoichiometric mixture, and the soot emission of CO 2 dilution was roughly 33.9% lower than that of EGR dilution at lean-burn mixture. In terms of engineering applications, the CO 2 dilution had more advantageous compared with EGR dilution in a GDI engine. But for obtaining the same combustion, the dilution rate for CO 2 dilution should be significantly increased than that of EGR dilution. [ABSTRACT FROM AUTHOR]

• Added CO 2 in a gasoline direct injection engine is proposed. • Combustion and emissions under stoichiometric mixture and medium load are studied. • The role of CO 2 of GDI engine at different injection timings is revealed. • Injection timing of added EGR > injection timing of added CO 2. • The reduction BSNO X is added EGR ≫ added CO 2 at same injection timing and added CO 2. CO 2 was introduced to intake, the effect of injection timing (IT) and CO 2 dilution on combustion and emissions behaviors of a stoichiometric gasoline direct injection engine at medium load was analyzed and compared in order to assess the role of CO 2 dilution under different ITs. Experimental results showed that for obtaining good combustion performance, IT CO2 = 0% > IT added EGR, CO2 = 15% > IT added CO2, CO2 = 15%. Peak cylinder pressure (PCP), peak heat release rate and peak cylinder temperature first increased and then decreased as retarding IT, and their corresponding angle crank had opposite trends. At a constant IT, the order of PCP was as follows: PCP CO2 = 0% > PCP added CO2, CO2 = 15% > PCP added EGR, CO2 = 15%. Added EGR or CO 2 would keep CA50 and CA05-90 away from top dead center. The COV imep first decreased and then increased with retarding IT. At IT = 240°CA BTDC, the BSCO added EGR, CO2 = 15% and BSCO added CO2, CO2 = 15% emissions were approximately 0.4 and 3 times higher than BSCO CO2 = 0% emission, respectively; the BSHC added EGR, CO2 = 15% and BSHC added CO2, CO2 = 15% emissions were approximately 4.8% and 11.9% higher than BSCO CO2 = 0% emission, respectively; and the BSNO X added CO2, CO2 = 15% and BSNO X added EGR, CO2 = 15% emissions were approximately 11.2% and 58.7% lower than BSNO X CO2 = 0% emissions, respectively. [ABSTRACT FROM AUTHOR]

• Simulated EGR using CO 2 in a GDI engine is proposed. • Combustion and emissions under stoichiometric mixture and low load are studied. • The role of CO 2 in an EGR of GDI engine at different spark timings is revealed. • The reduction BSNO X is actual EGR > simulated EGR (CO 2) ≈ retarded spark timing. • EGR reduces reaction rate of soot formation and rises the oxidation rate of soot. Exhaust gas recirculation (EGR) is one of the most effective measure to control NO X emissions in the engines. CO 2 was introduced to intake as simulated EGR (CO 2), the combustion and emissions behaviors of a stoichiometric GDI engine with simulated EGR (CO 2) at engine speed of 1500 rpm, engine load of 25% and different spark timings were studied experimentally. Experimental results show that EGR and retarded spark timing would slow the combustion. At the same EGR rate, the effect of actual EGR on combustion parameters is much greater than that of simulated EGR (CO 2). A large amount of inert gas in EGR will greatly aggravate combustion, leading to increase COV imep. The order of COV imep is actual EGR rate = 15% ≫ simulated EGR (CO 2) rate = 15% > EGR rate = 0%. Spark timing has little effect on BSCO and BSHC for with/without EGR at low load. At any constant spark timing, BSCO actural EGR rate = 15% ≫ BSCO simulated EGR (CO2) rate = 15% > BSCO EGR rate = 0%. BSNO X and soot emissions decrease significantly with retarding spark timing for with/without EGR. BSNO X and soot emissions show same tendencies with retarding spark timing and increasing EGR rate. BSNO X emissions is actual EGR > simulated EGR (CO 2) ≈ retarded spark timing. At a constant spark timing, soot actual EGR rate = 15% < soot simulated EGR (CO2) rate = 15% < soot EGR rate = 0%. EGR reduces reaction rate of soot formation and rises the oxidation rate of soot. [ABSTRACT FROM AUTHOR]

• Simulated EGR using CO 2 in a GDI engine is proposed. • Combustion and emissions under stoichiometric and lean-burn conditions are studied. • The role of CO 2 in an EGR of GDI engine at low load is revealed. • Simulated EGR (CO 2) deterioration combustion is weaker than actual EGR. • Effect law of simulated EGR (CO 2) on NO X and soot emissions is the same. Exhaust gas recirculation (EGR) is one of the most measure to decrease NO X emissions in the cylinder. CO 2 was introduced to intake charge as a simulated EGR (CO 2), the combined effects of excess air ratio and EGR rate on combustion and emissions behaviors of a gasoline direct injection (GDI) engine with simulated EGR (CO 2) at low load were analyzed and compared to assess the difference between actual EGR and simulated EGR (CO 2). The results show that EGR slows combustion, and simulated EGR (CO 2) deterioration combustion is weaker than actual EGR. The peak cylinder pressure, heat release rate and cylinder temperature of simulated EGR (CO 2) all increase and their phases all advance compare to actual EGR under the same EGR rate and excess air ratio. Combustion center and combustion duration for simulated EGR (CO 2) delay slowly with EGR rate at any excess air ratios. Simulated EGR (CO 2) can significantly improve the COV imep of the engine. For actual EGR rate > 10% and excess air ratio of 1.2, the COV imep sharply increases. Simulated EGR (CO 2) has a little effect on CO emission at lean-burn condition, and on HC emission at stoichiometric condition. The NO X and soot emissions decrease significantly with EGR rate under different forms of EGR and excess air ratios. At a fixed EGR rate, the soot emissions of simulated EGR (CO 2) is higher than that of actual under any excess air ratios. Added 10–15% CO 2 to intake charge, CO 2 as simulated EGR (CO 2) can be well applied in GDI engine. [ABSTRACT FROM AUTHOR]

Twin-spark plug synchronous ignition is an effective means of improving the stability of combustion and extending the lean-burn limit of the spark ignition engine. In this study, the distribution of mixture concentration, combustion, and emissions-related behaviors of a direct-injection twin-spark plug synchronous ignition methanol engine are numerically investigated to assess its lean-burn performance and solve for stable combustion under a medium compression ratio. The simulation results shows that the timing of the injection and ignition, and the distribution of flow velocity at ignition determine the distribution of the mixture concentration in the cylinder, which in turn affects the density of the flame surface and emissions. The delay ignition timing, the unburned methanol emissions increase significantly, while the nitrogen oxides emissions decrease rapidly. Optimal injection timing of 110°crank angle before top dead center and ignition timing of 21°crank angle before top dead center could obtain the best compromise of a medium compression ratio direct-injection twin-spark plug synchronous ignition methanol engine under steady-state lean-burn conditions. Thus, twin-spark plug synchronous ignition can ensure stable combustion and yield good performance with a medium compression ratio under lean-burn conditions. • Twin-spark plug synchronous ignition was proposed for methanol engine. • Methanol late-injection strategy under medium compression ratio was used. • Combustion of methanol engine at steady-state and lean-burn conditions was studied. • Injection and ignition timings determined the distribution of mixture concentration. • Optimal injection and ignition timings could obtain the best performance compromise. [ABSTRACT FROM AUTHOR]

Twin-spark plug synchronous ignition is an effective means of improving the stability of combustion and extending the lean-burn limit of the spark ignition engine. In this study, the distribution of mixture concentration, combustion, and emissions-related behaviors of a direct-injection twin-spark plug synchronous ignition methanol engine are numerically investigated to assess its lean-burn performance and solve for stable combustion under a medium compression ratio. The simulation results shows that the timing of the injection and ignition, and the distribution of flow velocity at ignition determine the distribution of the mixture concentration in the cylinder, which in turn affects the density of the flame surface and emissions. The delay ignition timing, the unburned methanol emissions increase significantly, while the nitrogen oxides emissions decrease rapidly. Optimal injection timing of 110°crank angle before top dead center and ignition timing of 21°crank angle before top dead center could obtain the best compromise of a medium compression ratio direct-injection twin-spark plug synchronous ignition methanol engine under steady-state lean-burn conditions. Thus, twin-spark plug synchronous ignition can ensure stable combustion and yield good performance with a medium compression ratio under lean-burn conditions. • Twin-spark plug synchronous ignition was proposed for methanol engine. • Methanol late-injection strategy under medium compression ratio was used. • Combustion of methanol engine at steady-state and lean-burn conditions was studied. • Injection and ignition timings determined the distribution of mixture concentration. • Optimal injection and ignition timings could obtain the best performance compromise. [ABSTRACT FROM AUTHOR]

• Model of optimal arrangement of twin-spark plug of methanol engine was built. • Ultra-lean burn conditions were selected for simulation evaluation. • Methanol late-injection strategy under medium compression ratio was used. • Optimal arrangement of twin-spark plug was A = 0.65. • Unburned methanol and soot emissions increased rapidly under A > 0.75. The effects of twin-spark plug arrangement on flame, combustion and emissions of a medium compression ratio direct injection methanol engine were numerically investigated. Computational results showed that at approximately A (ratio of distance of twin-spark plug and cylinder diameter) = 0.65, the burning and exothermic were the most reasonable compared to other twin-spark plug locations. A = 1.00 was the worst twin-spark plug arrangement. The maximum in-cylinder pressure and the maximum in-cylinder temperature were decreased with increasing A. Ignition delay were increased with increasing A. The A = 0.65 had the shortest combustion duration and the maximum heat release rate. The maximum in-cylinder pressure of A = 1.00 was approximately 57.5% lower than A = 0.25. The ignition delay of A = 1.00 was approximately 2.4 times longer than A = 0.25. The combustion duration of A = 0.67 was approximately 12% and 52.2% lower than A = 0.25 and A = 1.00, respectively. Unburned methanol and soot were increased gradually with increasing A, and at the A > 0.75, the unburned methanol and soot emissions were increased rapidly as increasing A. The unburned methanol of A = 1.00 was approximately 4.6 times higher than A = 0.25. The variations in emitted NO X emissions showed opposite tendencies with the variations in unburned methanol and soot emissions. The optimum arrangement of the twin-spark plug for application of actual engine was approximately A = 0.65. [ABSTRACT FROM AUTHOR]

Influences of ignition timing (IT) on combustion, carbon monoxide (CO) and nitric oxide (NO) regulated emissions and formaldehyde (HCHO) and unburned methanol (CH 3 OH) unregulated emissions in a hydrogen (H 2)/methanol dual-injection automobile engine under lean-burn condition were studied numerically. The results demonstrate that at lean-burn (excess air ratio = 2.0) condition, the peak cylinder pressure (PCP), peak heat release rate (PHRR) and peak cylinder temperature (PCT) all decrease with delayed IT, and their corresponding crank angles are also late; ignition delay (ID) and combustion duration (CD) decrease with delayed IT; CO, HCHO and CH 3 OH emissions increase with delayed IT, while NO emission decreases with delayed IT. At a fixed IT, PCP, PHRR and PCT for with adding 5 % H 2 (R H2 = 5 %) are higher than those for without adding H 2 (R H2 = 0 %), and their corresponding crank angles for R H2 = 5 % are earlier than those for R H2 = 0 %; ID and CD for R H2 = 5 % are lower than those for R H2 = 0 %. CO, HCHO and unburned CH 3 OH emissions for R H2 = 5 % are also much lower than those for R H2 = 0 %, while NO emission for R H2 = 5 % is also higher than that for R H2 = 0 %. The influence order of adding H 2 to reduce emissions of engine is: CO > HCHO > unburned CH 3 OH. • H 2 /methanol dual-injection was proposed to improve HCHO and unburned CH 3 OH emissions. • The role of H 2 -assisted combustion was revealed. • Influence of increasing H 2 on promoting combustion is obvious. • Influence order of adding H 2 to reduce emissions is: CO > HCHO > unburned CH 3 OH. [ABSTRACT FROM AUTHOR]

The impacts of excess air ratio (λ) on combustion, CO and NO regulated emissions, and formaldehyde (HCHO) and unburned methanol (CH 3 OH) unregulated emissions behaviors in a spark-ignition H 2 /methanol dual injection engine were studied numerically. The results show that the peak in-cylinder pressure (PIP), peak heat release rate (PHRR) and peak in-cylinder temperature (PIT) all decrease with the increase of λ , and their corresponding crank angles are also late; the ignition delay (ID) and combustion duration (CD) decrease with the increase of λ ; the CO, HCHO and CH 3 OH emissions increase with the increase of λ , while the NO emission decreases with the increase of λ. At a constant λ , the PIP, PHRR and PIT for with 5 % H 2 (R H2 = 5 %) are higher than those for without H 2 (R H2 = 0 %), and their corresponding crank angles for R H2 = 5 % are earlier than those for R H2 = 0 %; the ID and CD for R H2 = 5 % are lower than those for R H2 = 0 %. The CO, HCHO and CH 3 OH emissions for R H2 = 5 % are also much lower than those for R H2 = 0 %, while the NO emission for R H2 = 5 % is also higher than that for R H2 = 0 %. The impact order of adding H 2 to reduce emissions of H 2 /methanol dual-injection engine is: CO ≥ HCHO > unburned CH 3 OH. • H 2 -assisted combustion was proposed to improve the combustion and emissions of H 2 /methanol engine.. • The role of H 2 -assisted combustion was revealed.. • Adding H 2 is more beneficial to improve the firing characteristics under lean burn. • The impact order of adding H 2 to reduce emissions is: CO ≥ HCHO > unburned CH 3 OH. [ABSTRACT FROM AUTHOR]

• Radicals, combustion and unregulated emissions are numerically calculated. • OH, O, and H radicals obviously increase with increase of intake oxygen during cold start. • The generation and oxidation mechanism of formaldehyde is illuminated. • Formaldehyde and unburned methanol show an opposite trend with intake oxygen. Oxygen enrichment combustion is one of the attractive methods to improve combustion and reduce emissions in spark ignition engines. The effects of intake oxygen enrichment on intermediate radicals, combustion, and unregulated emissions of formaldehyde and unburned methanol during cold start were numerically calculated by using CFD simulation coupled with a detailed methanol chemical kinetic model for a DISI methanol engine. Results show that the concentration of OH, O, and H radicals during cold start is obviously increased and CA50 is slightly advanced with increase of intake oxygen concentration (C O2), resulting in accelerated chain reaction in methanol combustion, and further mitigating unburned methanol emissions. When C O2 varies from 21% to 36%, cylinder temperature increases due to the post-combustion. Cylinder temperature reaches the maximum value at 36% C O2. After further increasing C O2 to 41%, the in-cylinder temperature start to decrease as a result of the decreased OH concentration and inhibited post-combustion. In general, C O2 is the accelerant in formaldehyde formation at initial stage and in formaldehyde oxidization during post-combustion. By increasing C O2 , formaldehyde emission rises and unburned methanol emission diminishes during cold start. [ABSTRACT FROM AUTHOR]

Highlights • Hydrogen-enriched methanol combustion under lean burn condition was proposed. • Engine performances under different ignition timing and speeds were studied. • Added hydrogen can effectively improve combustion under middle and high speed. • Added hydrogen decreases CO and HC at low speed and various ignition timing. • Added hydrogen increases NO X and soot at high speed and various ignition timing. Abstract 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 COV imep. By comparison with cases without hydrogen, the COV imep 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. [ABSTRACT FROM AUTHOR]

Based on the methanol oxidation and NO X reaction mechanisms, we explored the effect of hydrogen addition on the methanol oxidation reaction mechanism. We used the PREMIX subroutine in Chemkin chemical reaction dynamics analysis software, and studied the effect of hydrogen addition numerically on the main intermediate and final products in methanol premixed laminar flames under lean burn and given initial conditions such as temperature and pressure. The combustion and emission parameters in the methanol engine were researched for the addition of hydrogen in different volume ratios. The simulation results show that hydrogen addition can accelerate the methanol oxidation reaction rate and that the reaction rate increased with increase in hydrogen addition in methanol premixed laminar flames. H, O, and OH radicals can accelerate the chemical reaction rate in the flame. The maximum mole fraction of CH 2 O decreases with increase in hydrogen addition, which shows that hydrogen addition can reduce CH 2 O and has a positive influence on the environment. Temperature has little effect on NO formation in the methanol–hydrogen premixed laminar flames; the mole fraction of NO decreases with increase in hydrogen addition. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Combustion, carbon monoxide (CO), Nitrous oxide (NO), formaldehyde (HCHO) and unburned methanol (CH 3 OH) 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 (NO X ) 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. [ABSTRACT FROM AUTHOR]

• Added CO 2 in a gasoline direct injection engine is proposed. • The peak NO X generation mixture is adopted. • The role of CO 2 dilution of gasoline direct injection engine is revealed. • Added CO 2 deterioration combustion is much smaller than that of added EGR. • Effect of added CO 2 on combustion of low load is even greater. In this paper, CO 2 was introduced to intake charge, the combustion and emissions behaviors between added CO 2 and added EGR (exhaust gas recirculation) in a gasoline direct injection (GDI) engine under the peak NO X generation mixture and at low and medium loads were analyzed and compared in order to assess the role of CO 2 in the intake charge of engine. Experimental results show that the combustion performances for added CO 2 was better than that of added EGR. The effect of added CO 2 on the combustion parameters at low loads was greater than that at medium loads. The coefficient of variation of indicated mean effective pressure almost did not change with increasing percentage of CO 2 under only added CO 2 and medium load. The effect of added CO 2 on combustion parameters was much less than added EGR. At a fixed CO 2 , CO and HC emissions for added CO 2 were lower significantly than those of added EGR at medium load, and vice versa on low load. Increasing CO 2 , the NO X emissions decreased significantly for added EGR and added CO 2 at any engine loads. At a fixed CO 2 , the NO X emissions for added CO 2 was higher obviously than that of added EGR at any engine loads. The soot emission was decreased slightly as increasing percentage of CO 2. [ABSTRACT FROM AUTHOR]

• Combustion of hydrogen/methanol dual-injection engines was studied under lean-burn. • Lean-burn limit was compared under different hydrogen addition ratios. • Ignition timing was optimized for different hydrogen addition ratios under lean-burn. • Hydrogen-enriched could expand the lean-burn limit to excess air ratio 2.95. • The critical hydrogen addition ratio for hydrogen-assisted combustion was ≤ 6%. 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. [ABSTRACT FROM AUTHOR]

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. • Nozzle spray-line distribution is numerically studied under lean burn conditions. • High compression ratio is used in direct-injection spark-ignition methanol engine. • Non-uniform spray-line nozzle is favor to form methanol-air stratified mixture. • Non-uniform spray-line nozzle of a 10-hole × 0.30 mm has a faster combustion process. • Ideal stratified mixture nozzle has lower unburned methanol, CO and soot emissions. [ABSTRACT FROM AUTHOR]

• Phasing of an ideal θ pmax and CA50 was used to determine optimal spark timing. • Spark timing under different H 2 addition ratios and equivalence rates was optimized. • The higher H 2 addition is, the later spark timing will be at same equivalence ratio. • Using spark timing by θ pmax could achieve the best compromise of performance. The combustion phase of the maximum in-cylinder pressure (θ pmax) and 50% heat release rate position (CA50) are often used to evaluate the reasonableness of the engine combustion. Spark timing is a decisive parameter that influences θ pmax and CA50 of spark-ignition engine. A H 2 port-injection and methanol direct-injection dual-fuel engine was adopted to study the adjustment spark timing under low engine speed, lean-burn and methanol late-injection strategy by application constant θ pmax and CA50 combustion center. The performances of the adjustment spark timing by constant θ pmax and CA50 combustion center was compared with performances of maximum brake torque (MBT) spark timing under equivalence ratio 1.0. The results show that using constant θ pmax 16 °CA ATDC combustion center, the optimal spark timing was advanced as decreasing equivalence ratio. Using constant CA50 of 10 °CA ATDC combustion center, the optimal spark timing was also advanced as decreasing equivalence ratio. The higher the H 2 addition ratio is, the later the optimal spark timing will be at same equivalence ratio. The optimal spark advance for addition H 2 is smaller than that of pure methanol, and the optimal spark advance for 6% addition H 2 is smaller than that of 3% addition H 2. The adjustment spark timing by θ pmax 16 °CA ATDC has good regularity. The adjustment spark timing by CA50 10 °CA ATDC is almost random. Using adjustment spark timing by θ pmax could achieve the best compromise of engine performance for with/without H 2 addition methanol engines. [ABSTRACT FROM AUTHOR]

• H 2 -enriched methanol was proposed to extend lean-burn limit. • Lean-burn ability under different spark timings and H 2 addition ratios was clarified. • H 2 -enriched can expand lean-burn limits form equivalence ratio 0.625 to 0.455. • COV imep could be controlled to within 10% under lean mixture and 6% of H 2 added. The addition of H 2 is an effective way to enhance the speed of propagation of a flame and extend the lean-burn limit of spark ignition (SI) engines. An H 2 port-injection and methanol direct-injection dual-fuel SI engines were used in this study to investigate the effect of the equivalence ratio on the combustion and emissions characteristics of the engine at low speed using the late injection strategy for methanol. The results show that 3%–6% of H 2 -enriched methanol can effectively expand the lean-burn limit from an equivalence ratio of 0.625 of pure methanol to that of 0.455. The spark timing of H 2 addition must be optimized by different equivalence ratios and ratios of H 2 addition to implement ideal combustion phasing at 16°CA ATDC and 10°CA ATDC of p max and HRR max , respectively. H 2 addition can significantly shorten both CA0-10 and CA10-90, and can quickly advance CA50. For 6% of H 2 added, when the equivalence ratio was over 0.5, the COV imep was below 3.5%. This addition significantly improved the lean-burn characteristics of the H 2 /methanol SI engine. BSHC emissions with the addition of 6% H 2 was much lower than that of the pure methanol engine at equivalence ratios of over 0.625. When H 2 was added, BSCO emissions increased rapidly in terms of both lean and stoichiometric equivalence ratios, compared with the case when no H 2 was added. [ABSTRACT FROM AUTHOR]

The effects of plasma-assisted ignition and combustion on the ignition-delay time (T id) and intermediates in methanol combustion were simulated numerically through a chemical-kinetics mechanism of methanol oxidation. Plasma-assisted ignition can considerably shorten the T id. Plasma-assisted ignition is more conducive to a low temperature and the lean combustion of a methanol-air mixture. According to the shortest T id , the active particle order is: O < CH 3 O < 220 Td < H < OH < CH 2 OH < CH 3 < autoignition. The concentration of O atoms in active particles affects the T id shortening. Plasma-assisted combustion can significantly shorten the time for the system temperature to reach a maximum. The concentrations of the reactants CH 3 OH and O 2 decrease sharply for autoignition after the ignition-delay period, and the products CO, CO 2 and H 2 O increase rapidly. In plasma-assisted combustion, the addition of active particles significantly increases the rate of chemical reaction of consumption of O 2 , promotes the rapid redox reaction of methanol–air mixtures, oxidizes methanol fuel to CO 2 and H 2 O more rapidly, and accelerates combustion. The sensitivity coefficients of temperature and T id for plasma-assisted combustion are lower than those for autoignition. • Plasma-assisted combustion in methanol-air mixtures is numerical simulated. • Plasma-assisted ignition can significantly shorten ignition delay time. • The O atom plays a key role in shortening ignition delay time. • The evolution mechanism of intermediates is clarified. • Sensitivity coefficient for plasma-assisted combustion is lower than autoignition. [ABSTRACT FROM AUTHOR]

• Lean-burn strategy of H 2 /methanol dual-fuel dual-injection engines is proposed. • Lean-burn characteristics of homogeneous and stratified combustion modes are compared. • HPI + MDI engines for 6% H 2 addition can effectively extend lean-burn limit to excess air ratio 2.2. • The BSHC and BSCO emissions of HPI + MPI engines are lower than these of HPI + MDI engines. • The BSNO X and soot emissions of HPI + MPI engines are higher than that of HPI + MDI engines. Lean-burn is an effective way to improve thermal efficiency and reduce emissions of spark-ignition (SI) engines. A hydrogen (H 2) enrichment combustion strategy can extend the lean-burn limits of SI engines. Two engines equipped with hydrogen and methanol dual-port injection (HPI + MPI) and hydrogen port injection plus methanol direct injection (HPI + MDI) were used to evaluate the lean-burn capability of SI engines. The lean-burn characteristics of homogeneous and stratified combustion modes were compared. The results showed that H 2 addition was more conducive to extending the lean-burn limit of the direct-injection methanol engine and achieving high indicated mean effective pressure (IMEP) than the port-injection methanol engine. HPI + MDI engines with 6% H 2 addition effectively extended the lean-burn limit to an excess air ratio of 2.2. H 2 addition compensated for the power drop caused by the decrease in volumetric efficiency and speed up combustion under lean-burn conditions. H 2 addition could also realize stable combustion under super lean-burn conditions for HPI + MDI engines. The BSHC and BSCO emissions of HPI + MPI engines were lower than those of HPI + MDI engines, but the BSNO X and soot emissions were higher. H 2 addition decreases BSCO 2 emissions at the same excess air ratio for both the HPI + MPI and HPI + MDI engines. [ABSTRACT FROM AUTHOR]