Unburned Methanol Emissions Research Articles

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.

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

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

Numerical research on combustion and emissions behaviors of a medium compression ratio direct-injection twin-spark plug synchronous ignition methanol engine under steady-state lean-burn conditions

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.

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.

Numerical study of twin-spark plug arrangement effects on flame, combustion and emissions of a medium compression ratio direct-injection methanol engine

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 NOX 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.

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.

Evaluating the In-Service Emissions of High-Mileage Dedicated Methanol-Fueled Passenger Cars: Regulated and Unregulated Emissions

This paper reports the regulated, unregulated, and particle number emissions from six high-mileage, China-4 compliant, dedicated methanol taxis over the new European driving cycle. Compared to new vehicles, carbon monoxide, total hydrocarbons, and nitrogen oxides emissions from in-use methanol taxis increased by 76.1%, 40.2%, and 179.8%, respectively. Still, they managed to meet China-4, indicating good in-service conformity. In the test fleet, the test vehicles with longer mileage inclined to emit higher carbon monoxide and total hydrocarbons emissions. Formaldehyde emissions from these field-aged taxis ranged from 1.06 to 2.33 mg/km, which were similar to or lower than those from previously reported pre-Euro-5 gasoline vehicles. One of the six test vehicles produced extraordinarily high unburned methanol emissions, which was about ten times higher than the rest of the properly operating vehicles due to possible misfire, suggesting that unburned methanol will be the primary stress for future methanol applications. Compared to the regulated emissions, formaldehyde and unburned methanol emissions deteriorated at faster rates along with catalyst aging. Particle number emissions from these methanol taxis remained low even after high-mileage driving, suggesting the compatibility of methanol fueling in future particle number compliance.

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.

Numerical investigation of intake oxygen enrichment effects on radicals, combustion and unregulated emissions during cold start in a DISI methanol engine

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 (CO2), resulting in accelerated chain reaction in methanol combustion, and further mitigating unburned methanol emissions. When CO2 varies from 21% to 36%, cylinder temperature increases due to the post-combustion. Cylinder temperature reaches the maximum value at 36% CO2. After further increasing CO2 to 41%, the in-cylinder temperature start to decrease as a result of the decreased OH concentration and inhibited post-combustion. In general, CO2 is the accelerant in formaldehyde formation at initial stage and in formaldehyde oxidization during post-combustion. By increasing CO2, formaldehyde emission rises and unburned methanol emission diminishes during cold start.

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.

Effects of injection timing of methanol and LPG proportion on cold start characteristics of SI methanol engine with LPG enriched port injection under cycle-by-cycle control

A liquefied petroleum gas (LPG) enriched port injection start aid was used to improve firing and emissions characteristics and overcome cold start difficulties for spark ignition (SI) methanol engines at low ambient temperature. The effects of injection timing of methanol and LPG addition fraction on cold start firing; and hydrocarbon (HC), formaldehyde, and unburned methanol emissions were investigated experimentally using cycle-by-cycle control strategy. Injection timing of methanol significantly affected cold start firing behavior for constant injection timing of LPG. At optimal injection timing of methanol the most fuels enter into the cylinder on time to realize ideal firing of the next cycle combustion after fuel injection. Sufficient LPG addition can ensure reliable cold start firing. The methanol engine obtained lowest HC and unburned methanol, and highest formaldehyde tailpipe emissions for optimal injection timing of methanol. Increasing LPG addition fraction significantly decreased HC and unburned methanol tailpipe emissions and increased formaldehyde emission rapidly. Formaldehyde and unburned methanol tailpipe emissions showed opposite tendencies with injection timing of methanol and LPG addition fraction, whereas HC and unburned methanol tailpipe emissions showed similar tendencies during cold start.

Comparison of the conversion efficiency of DOC and DPOC to unregulated emissions from a DMDF engine

The experimental research on reducing unregulated emissions (included unburned methanol, formaldehyde, formic acid, 1,3-butadiene, benzene and toluene) of diesel/methanol dual fuel (DMDF) engine with different after-treatment devices was carried out on a turbocharged inter-cooling diesel engine. The DMDF engine was operated under 25%, 50%, 75% and 100% of full load at the engine speed of 1660rpm and 2090rpm with the same injection parameters for the different methanol substitution ratios (MSR). Unregulated emissions of DMDF engine with and without after-treatment devices single diesel oxidation catalyst (DOC) and DOC coupled with particulate oxidation catalyst (DPOC) were studied in comparison. The results show that compared with pure diesel mode, the unregulated emissions tested in this research are all increased in different degrees when the engine operates on diesel/methanol dual fuel mode, and they are all increased with increasing fumigation methanol. The conversion efficiency of DPOC for unregulated emissions tested in this research is higher than that of single DOC. Single DOC could significantly reduce the unburned methanol, 1,3-butadiene and formic acid emissions from DMDF engine, especially at medium and high load when exhaust gas temperature is relative high, but formaldehyde emissions after DOC are increased at low load. After the catalytic oxidation of DPOC, the unburned methanol, formaldehyde, formic acid, benzene and toluene emissions of diesel/methanol dual fuel mode under all load at the speed of 1660rpm, all except low load at the speed of 2090rpm are not much different from pure diesel mode.

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 of formaldehyde and unburned methanol emissions of direct injection spark ignition methanol engine under cold start and steady state operating conditions

The effects of overall equivalence ratio, injection timing, and ignition timing on formaldehyde and unburned methanol emissions, cylinder temperature histories, and formaldehyde emission histories of a spark ignition direct injection stratified charge methanol engine during cold start and steady state conditions were simulated using computational fluid dynamics coupling the methanol chemical kinetics reaction mechanism. The model results show that the overall equivalence ratio is less than 0.43, and unburned methanol significantly higher for cold start mode. For steady state mode, when the overall equivalence ratio is less than 0.4, formaldehyde and unburned methanol emissions increase rapidly. When the overall equivalence ratio is larger than 0.4, formaldehyde and unburned methanol emissions are very low. Formaldehyde and unburned methanol emissions for steady state mode are significantly lower than for cold start mode. For steady state mode at engine speed 1600rpm and brake mean effective pressure 0.67MPa formaldehyde and unburned methanol emissions are reduced 90% and 98%, respectively, compared to cold start mode at the same overall equivalence ratio (0.5). Cylinder temperature is the main factor that affects formaldehyde generation and consumption. There is a rapid decrease due to oxidation at the corresponding position of the maximum cylinder temperature, after which formaldehyde is quickly generated for any operating conditions.

Modeling of the overall equivalence ratio effects on combustion process and unregulated emissions of an SIDI methanol engine

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.

Effects of engine misfire on regulated, unregulated emissions from a methanol-fueled vehicle and its ozone forming potential

Methanol is a feasible and promising alternative fuel for passenger cars, particularly in China. However, methanol-fueled vehicles struggle with stronger low-temperature operating instability and increased chance of misfire. In prior publications, the impacts of engine misfire on the regulated and unregulated emissions from methanol-fueled vehicles have been merely discussed. In this paper, regulated emissions, unburned methanol, carbonyl and VOC emissions from a China-5 (equivalent to Euro-5b+IUPR) certificated methanol-fueled car were measured over new European driving cycle (NEDC). By using a SAE J2901-compatible generator, two misfire rates (6% and 9%) were employed to mimic ordinary and severe engine malfunction statuses. Emission results were also put into comparison with the current Euro-5 and the upcoming Euro-6c OBD threshold limits, and used to estimate Carter MIR-based ozone forming potential. The results demonstrated that, both CO and THC emissions increased with misfire rate while NOx emission persistently decreased with intensified engine misfire. Even with a misfire rate up to 9%, all the regulated emissions were significantly lower than their thresholds regulated in Euro-5 and Euro-6c, which meant the current OBD requirements were too tolerant for methanol vehicles. It is proposed that, countries regarding methanol as a future option, shall promulgate methanol-specific emission standards in advance. Unburned methanol emission increased by at least 1.6 and 5.7 times when misfire rates of 6% and 9% were used. Both carbonyl and VOC emissions increased corresponding to higher misfire rates. Formaldehyde and toluene were found the key pollutants of carbonyls and VOCs. An increase in anticipated ozone forming potential (OFP) together with a decrease in specific reactivity (SR) was also noticed with the rising of misfire rate. Among all the pollutants, CO, toluene, xylene and formaldehyde were the chief species contributing to secondary ozone formation.

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.