Flame Propagation Periods Research Articles

Effect of excess air/fuel ratio and methanol addition on the performance, emissions, and combustion characteristics of a natural gas/methanol dual-fuel engine

To investigate the effect of excess air/fuel ratio (λ) and methanol addition on the combustion characteristics, performance, and emissions, a heavy-duty, turbo-charged, six-cylinder natural gas engine was modified into a natural gas/methanol dual-fuel engine with a methanol port-fuel injection system. The engine speed was maintained at a constant value of 1600 r/min, the engine load was kept at a low value with the brake mean effective pressure at 0.387 MPa, and the spark timing was maintained near the optimized brake thermal efficiency (ηet). The results indicated that the addition of methanol decreased the flame development period (CA0–10) and flame propagation period (CA10–90), leading to an increased ηet and a decreased equivalent brake specific fuel consumption (BSFC), along with reduced total hydrocarbon emissions. Additionally, with an increase in λ, the burning rate of natural gas decreased owing to the decreased energy density and combustion temperature and pressure. However, ηet increased and the equivalent BSFC decreased at the lean-burn condition. The total hydrocarbon emissions increased while the nitrogen oxide emissions decreased with an increase in λ. The decreased burning rate of natural gas at the lean-burn condition can be increased by adding methanol, particularly when λ = 1.5 and 1.6. The lean-burn capability of natural gas can be improved by adding methanol.

Comparative study of combustion process and cycle-by-cycle variations of spark-ignition engine fueled with pure methanol, ethanol, and n-butanol at various air–fuel ratios

The combustion characteristics and cycle-by-cycle variations of a spark-ignition engine fueled with pure methanol, ethanol, and n-butanol were comparatively analyzed. All experiments were performed using a natural gas/alcohols dual-fuel engine with the alcohol fuel energy substitution ratio of 100%. The engine was kept under a low load with a brake mean effective pressure of 0.387 MPa. Engine speed was kept constant at 1600 r/min and air–fuel ratio (λ) was set in the range of 1–1.5 and varied in intervals of 0.1. The results showed that the pure methanol fuel yielded the highest peak cylinder pressure (Pmax) and peak heat-release rate (HRRmax) of the engine, followed by ethanol and then n-butanol. Moreover, Pmax and HRRmax decreased with the increase in λ, and the corresponding crank angles were reduced for the three primary alcohol fuels. The flame-development and flame-propagation periods of methanol were shorter than those of ethanol and n-butanol. The indicated mean effective pressure (IMEP) was distributed in a wider range with the increase in λ for the engine fueled with ethanol and n-butanol. However, for methanol, the IMEP was distributed in a relatively narrow range under all conditions of λ. When λ was increased from 1.0 to 1.5, the coefficient of variation in IMEP (COVIMEP) of methanol increased from 1.36% to 2.65%, the COVIMEP of ethanol increased from 1.71% to 10.46%, and the COVIMEP of n-butanol increased from 2.06% to 15.66%. Thus, methanol had a higher burning rate, lower cycle-by-cycle variations, and a better lean-burn capability than that of ethanol and n-butanol.

Effect of different hydrogen blending ratios on combustion process of gasoline‐fueled rotary engine

The pre‐eminent gasoline rotary engine may be criticized for its unsatisfactory fuel consumption rate and unburnt emissions. The clean and renewable hydrogen fuel is a promising alternative for conventional fuels to improve the combustion process and power performance of the rotary engine. In this article, highly advanced numerical simulation was used to obtain some pivotal results such as the distribution of combustion intermediates, the turbulent kinetic energy, the kinetic rate of reactions, and the fuel concentration fields which are difficult to experimentally achieve. An experimentally validated three‐dimensional dynamic simulation model of a rotary engine coupled with chemical kinetics skeletal mechanism was set up to exactly investigate the effects of hydrogen blending on the combustion process, power performance, and pollutant emissions. The results showed that with the increase of hydrogen mixing ratio, the average pressure and the peak pressure increased in the combustion process. Meanwhile, more combustion active intermediates were generated in both the flame development period and flame propagation period. The mass fraction of OH and H radicals has an increase of 36% and 34%, respectively. The fuel combustion rate rose and the turbulent kinetic energy increased which are conducive to improving flame diffusion in the rear part of the chamber and thus facilitate the complete combustion of the fuel. Moreover, the hydrogen blending led to an effective reduction in the CO emission of gasoline‐fueled rotary engine; however, the NO emission slightly increased due to the rise of temperature in cylinder. © 2019 American Institute of Chemical Engineers Environ Prog, 38:e13146, 2019

Realizing low emissions on a hydrogen-fueled spark ignition engine at the cold start period under rich combustion through ignition timing control

This paper analyzed low emissions on a hydrogen-fueled spark ignition (SI) engine at the cold start period under rich combustion through ignition timing (IT) control. Cold start characteristics of hydrogen-fueled engine were investigated experimentally. The study was performed under different IT. The results demonstrated that when excess air ratio (λ) was 0.7 and IT varied from 25 °CA BTDC to 10 °CA ATDC, the peak cylinder pressure of the first cycle and the successful start time (SST) of hydrogen engine first increased and then decreased with the retard of IT. At 15 °CA BTDC, the hydrogen engine gained the shortest SST and the highest cylinder pressure in the first cycle. Flame development period (CA0-10) first shortened and then lengthened, and flame propagation period (CA10-90) prolonged when IT gradually retarded. The average NOx emissions efficiently reduced by 90.2%, HC and CO emissions caused by the evaporated lubricant oil reduced individually by 33.8% and 19.7% in the first 6 s during the cold start process with the retard of IT. Especially when IT delayed from 25 °CA BTDC to 15 °CA BTDC, the effect of IT on HC emissions was significant.

Experimental investigation on performance and combustion characteristics of spark-ignition dual-fuel engine fueled with methanol/natural gas

This study aims to evaluate the performance, emissions, and combustion characteristics of a methanol/natural gas dual-fuel spark-ignition engine by conducting several experiments. A heavy-duty natural gas engine is modified by adding a methanol port-injection system to accelerate the burning rate, increase the thermal efficiency, and reduce the hydrocarbon emission. The effects of the methanol energy substitution ratio (MSR) on the brake thermal efficiency, heat release rate, peak cylinder temperature, flame development period, flame propagation period, and emissions are investigated under light, medium, and heavy loads (brake mean effective pressures of 0.387, 0.775, and 1.163 MPa, respectively) at an engine speed of 1600 rpm and a relative air/fuel ratio of 1.3. The results show that the peak cylinder pressure, peak cylinder temperature, and heat release rate increase with an increase in the MSR. A larger MSR leads to a shorter flame development period and flame propagation period as well as earlier combustion phasing. In addition, the brake thermal efficiency increases and the equivalent brake specific fuel consumption decreases significantly with methanol enrichment under the three engine load conditions. For exhaust emissions, the brake specific total hydrocarbon emission decreases while the brake specific nitrogen oxide emission increases slightly with an increase in the MSR. For cycle-by-cycle variation, the coefficient of variation in the indicated mean effective pressure increases slightly with an increase in the MSR. In addition, the peak ringing/knocking intensity is found to be 2.05 MW/m2 that is much less than the critical knocking point (5 MW/m2). Therefore, there was no knocking throughout the entire experiment.

Effects of spark timing and methanol addition on combustion characteristics and emissions of dual-fuel engine fuelled with natural gas and methanol under lean-burn condition

This paper aimed to study the effects of spark timing and methanol addition on the combustion characteristics and emissions of a natural gas/methanol dual-fuel engine. The engine speed is maintained at 1600 rpm and the brake mean effective pressure (BMEP) is maintained at 0.387 MPa with an excess air/fuel ratio of 1.3. The methanol energy substitution ratio (MSR) is set to 0%, 7.5%, and 14.5%. The spark timings are varied from 18 °CA to 38 °CA before the top dead centre, in intervals of 4 °CA. The results demonstrate that for a specific spark timing, the methanol addition increases the peak cylinder pressure, the maximum of the heat release rate, and the peak cylinder mean temperature. Concurrently, it decreases the flame development period (CA0-10) and the flame propagation period (CA10-90) with an increase in the MSR. An improvement in the brake thermal efficiency (BTE), a reduction in the total hydrocarbon (THC) emission, and an increase in the nitrogen oxide (NOX) emission are achieved using methanol enrichment. In addition, the effect of these trends is more pronounced with an increase in MSR. In contrast, for a specific MSR, a spark timing advance increases the peak cylinder pressure and temperature, while decreasing the exhaust temperature under an identical BMEP. Moreover, the spark timing at the maximum BTE retards as MSR increases.

A comparative study on performance of the rotary engine fueled hydrogen/gasoline and hydrogen/n-butanol

The comparative study on performance of the hydrogen/gasoline and hydrogen/n-butanol rotary engines was conducted in the present paper. Considering the stable operation of the engine, for both hydrogen/gasoline case and hydrogen/n-butanol case, the operating conditions were set at: 4000 rpm (engine speed), 35 kPa (intake pressure) and 30 °CA BTDC (spark timing). The total excess air ratio of mixture was maintained at 1.0 through all the tests. The testing results displayed that hydrogen enrichment improved performance of both gasoline and n-butanol rotary engines. To be more specific, brake thermal efficiency was increased, flame development and propagation periods were shortened, the coefficient of variation in flame propagation period was decreased, and the emissions of HC and CO were decreased. NOx emissions were mildly increased after hydrogen addition. Besides, hydrogen/n-butanol rotary engine possessed the similar performance to hydrogen/gasoline rotary engine.

Realizing low NOx emissions on a hydrogen-fuel spark ignition engine at the cold start period through excess air ratios control

In this paper, the effects of excess air ratios (λ) on nitric oxide (NOx) emissions of a hydrogen-fueled spark ignition engine in the cold start period are studied. Cold start characteristics of hydrogen-fueled engine were investigated experimentally. The study was performed under different λ. The experimental results showed that, when λ declined from 1.6 to 0.7, the peak engine speed within the first 6 s increased and in-cylinder pressure in the first cycle raised firstly then decreased slightly while the flame development and propagation periods shortened, and the exhaust temperature at the 6th s raised from 329 K to 355 K. In addition, NOx emissions obviously decreased, whereas hydrocarbon (HC) and carbon monoxide (CO) emissions caused by the evaporated lubricant oil increased by decreasing λ within the first 6 s.

An experimental analysis of hydrogen enrichment on combustion characteristics of a gasoline Wankel engine at full load and lean burn regime

In this paper, a gasoline Wankel engine was modified and equipped with self-developed hybrid electronic control unit to experimentally investigate the effect of hydrogen-enrichment level on combustion characteristics of a gasoline Wankel engine at wild open throttle position and lean burn regime. Testing were carried out under constant engine speed of 3000 rpm and the lean operating limit of the original gasoline engine. The spark timing was set at 15 °BTDC. The hydrogen energy fraction in the intake was gradually increased from 0% to 10%. The results showed that hydrogen enrichment was effective on improving the combustion process through the shortened of the flame development and the flame propagation periods, advancing the central heat release, increasing the HRRmax and reducing the cyclic variation proportionally to the amount of hydrogen added to the air fuel mixture. Furthermore, increasing hydrogen fraction in the intake improves the engine economy by reducing the cooling loss.

Performance of a hydrogen-blended gasoline direct injection engine under various second gasoline direct injection timings

The performance of a hydrogen-blended gasoline direct injection engine under various second gasoline direct injection timings is investigated on a modified commercial gasoline direct injection engine. All tests are carried out at a typically congested city-driving condition using lean burn and split gasoline direct injection modes. Results show that under pure gasoline fuel supply mode, brake mean effective pressure, brake thermal efficiency, flame development period, flame propagation period, and maximum in-cylinder pressure vary obviously with various second gasoline direct injection timings and the best second gasoline direct injection timing for engine performance is 130 CAD before top dead center. Blending hydrogen could weaken variations of engine performance related parameters caused by changing second gasoline direct injection timing compared to that under pure gasoline mode. Besides, blending hydrogen could also reduce flame development and propagation periods, and enhance the maximum in-cylinder pressure under the same second gasoline direct injection timing. With hydrogen addition, the coefficient of variations in indicated mean effective pressure drops to less than 1.1%, but second gasoline direct injection timing has no obvious effect on it any more. Besides, adding hydrogen could reduce hydrocarbon and carbon monoxide emissions by 33.10% and 18.28% in average, respectively. Particulate number has a reduction of order of magnitudes (∼108 to ∼106 n/cm3 in average). With hydrogen addition, nitrogen oxides emissions increase.

Effect of ignition timing on performance of a hydrogen-enriched n-butanol rotary engine at lean condition

Ignition timing is an important parameter for spark-ignited engine. Hydrogen replenishment effectively improves the performance of engine. This paper experimentally investigated the impact of ignition timing on performance of a hydrogen-enriched n-butanol rotary engine. For this purpose, a rotary engine installed with a dual-fuel (hydrogen and n-butanol) port injection system was specially developed. An electronic management module was solely developed to control the fuel injection, excess air ratio and hydrogen proportion. In this experiment, the engine was run at 4000 rpm, an intake pressure of 35 kPa and an excess air ratio of 1.10. Hydrogen volume ratio was set at 0% and 3%, respectively. When hydrogen fraction was changed, n-butanol injection was also adjusted to make excess air ratio be 1.10. For 0% and 3% hydrogen addition, ignition timing was severally varied from 35 to 51°CA BTDC and 29 to 45°CA BTDC with an interval of 2°CA. Experimental results showed that with the increase of ignition advance, both peak chamber pressure and temperature were increased, brake thermal efficiency was initially ascended and then declined. Flame development period was prolonged whereas flame propagation period was shortened as ignition advance increase. Cyclic variation was initially weakened and then deteriorated by advancing ignition. HC and NOx emissions were reduced after retarding ignition timing. Ignition timing had little influence on CO emission.

Idle performance of a hydrogen rotary engine at different excess air ratios

Rotary engine has flat chamber and longs for fuel with high flame speed and small quenching distance. Hydrogen has many excellent characteristics that are suitable for the rotary engine. In this paper, the performance of a rotary engine fueled with pure hydrogen at different excess air ratios was experimentally investigated. The investigation was carried out on a single-rotor hydrogen-fueled rotary engine equipped with port fuel injection system. An online electronic control module was used to govern the hydrogen injection duration and excess air ratio. In this study, the engine was operating at the idle speed of 3000 rpm and different excess air ratios varied from 0.993 to 1.283. The test results demonstrated that the fuel energy flow rate of the hydrogen rotary engine and engine stability were reduced with the increase of excess air ratio. When the excess air ratio increased from 0.993 to 1.283, the hydrogen energy flow rate was decreased from 14.91 to 11.55 MJ/h. Both the flame development and propagation periods were increased with excess air ratio. CO emission was negligible, but HC, CO2 and NOx emissions were still detected due to the evaporation and possible burning of the lubrication-used gasoline, and oxidation reaction of nitrogen of the intake air.

Investigation on combustion and emissions characteristics of a hydrogen-blended n-butanol rotary engine

In this paper, a rotary engine equipped with an n-butanol and hydrogen port-injection system was developed to investigate the combustion and emissions characteristics of a hydrogen-blended n-butanol rotary engine at part load and stoichiometric conditions. A self-developed hybrid electronic control unit was adopted to adjust the injection durations of n-butanol and hydrogen. The rotary engine was run under the conditions of 4000 rpm, a manifold absolute pressure of 35 kPa and a fixed spark timing of 45 °CA before the top dead center during the whole testing operation. The hydrogen volumetric fraction in the total intake was varied from 0% to 6.30%. The test results manifested that the brake thermal efficiency and chamber temperature were simultaneously increased with hydrogen addition. The hydrogen supplement obviously shortened flame development and propagation periods. Both chamber pressure integral heat release fraction versus crank angle were increased when the hydrogen fraction was enhanced. HC emissions were reduced by 54.5% when hydrogen volume fraction was raised from 0% to 6.30%, CO and CO2 emissions were also reduced after increasing hydrogen blending fraction. NOx emissions were mildly elevated due to the improved chamber temperature.

Reducing cyclic variation of a gasoline rotary engine by hydrogen addition under various operating conditions

In the present paper, the cyclic variations of a hydrogen-blended gasoline rotary engine operated under various conditions were experimentally investigated. The experiments were carried out on a modified hydrogen-gasoline dual-fuel rotary engine equipped with an electronically-controlled fuel injection system. An electronic control module was specially made to command the fuel injection, excess air ratio and hydrogen volumetric fraction. The tested engine was first run at idle condition with a speed of 2400 rpm and then operated at 4500 rpm to investigate the cyclic variations of a hydrogen-enriched gasoline rotary engine under different hydrogen volumetric percentages in the total intake, excess air ratios and spark timings. The experimental results demonstrated that the coefficient of variations (in peak pressure, engine speed, flame development period and flame propagation period) of the gasoline rotary engine were distinctly decreased with the increase of hydrogen volume fraction under all the tested conditions. In particular, at idle and stoichiometric conditions, the coefficient of variation in CA0-10 and CA10-90 were reduced from 9.25% to 5.01%, 15.40% to 8.70%, respectively.

Investigation on performance of a hydrogen-gasoline rotary engine at part load and lean conditions

Lean combustion is a promising method for getting ameliorate engine performance. However, due to the small flammability of gasoline and elongated combustion chamber of rotary engine, gasoline rotary engine tends to encounter partial burning and even misfire when mixtures are dilute. Hydrogen (H2) occupies many advantages that may remit the aforementioned problems. For this motivation, a rotary engine installed gasoline-H2 port-injection system was developed to explore the performance of rotary engine fueled with H2-gasoline blends at part load and lean conditions. A speed of 4500rpm, a manifold absolute pressure (MAP) of 35kPa and a spark advance of 25°CA were adopted for this research. Hydrogen volume fraction (αH2) was kept at 0, 3% and 6%, respectively. Excess air ratio (λ) was gradually enlarged from 1.00 with a step of 0.05. For a given λ, when αH2 was increased, the results were showed subsequently. Peak chamber pressure was increased and its corresponding crank angle was advanced. Brake mean effective pressure, peak combustion temperature and brake thermal efficiency were simultaneously increased. Flame development and propagation periods, cooling loss and cyclic variation were reduced. HC and CO emissions were lessened whereas NOx emissions were heightened due to the raised combustion temperature.

Effect of spark timing on performance of a hydrogen-gasoline rotary engine

This paper aimed to study the effect of spark timing on performance of a hydrogen-gasoline dual-fuel rotary engine. For this aim, a modified rotary engine equipped with a dual-fuel port injection system was developed. An electronic management module (ECM) was specially made to command the fuel injection, excess air ratio and hydrogen volumetric fraction. In this study, the engine was operated at 4500rpm with a manifold absolute pressure (MAP) of 35kPa. Hydrogen volumetric percentage of total intake was kept at 0%, 3% and 6%, severally. When the hydrogen volumetric percentage was changed, the gasoline fraction was also adjusted to keep the mixture at the stoichiometric. For a specified hydrogen volumetric fraction, the ignition timing was varied from 24 to 42°CA BTDC (before top dead center) with a fixed interval of 2°CA. Experimental results showed that for a specific hydrogen volumetric percentage, the peak combustion pressure and chamber temperature were increased, brake thermal efficiency was first increased and then decreased with the increase of spark advance. Advancing spark timing caused the increased flame development period, the decreased flame propagation period and exhaust temperature. Cyclic variation was initially weaken and then deteriorated after raising spark advance. HC and NOx emissions were reduced after retarding spark timing. Spark timing had little effect on CO emission.

Improving idle performance of a hydrogen-gasoline rotary engine at stoichiometric condition

Because of the unusual structure chamber compared with traditional engines, gasoline rotary engine always encounters partial burning and increased noxious emissions at the idle. Hydrogen-addition could enhance the characteristics of combustion and emissions of sparked-ignited engines at idle. A modified gasoline rotary engine with electronic spark control and fuel (gasoline and hydrogen) port-injection system was developed to study the impact of hydrogen-addition on idle performance of a gasoline rotary engine. A hybrid electronic control unit was invented to manage the spark, fuel injection, hydrogen volume fraction of the total intake and overall excess air ratio. In this study, the engine was operating at the idle speed of 2400 rpm and stoichiometric conditions. The hydrogen volume fraction was gradually varied from 0% to 6.8%. Results showed that the coefficient of variation in speed and fuel energy flow rate were both decreased after the hydrogen-addition. Flame development and propagation periods were shortened owning to hydrogen-addition. The peak chamber temperature was enhanced after the hydrogen-addition due to the high adiabatic flame temperature of hydrogen. Cooling loss was dropped when hydrogen was added into gasoline. HC, CO and CO2 emissions were reduced by 79.4%, 86.0% and 25.9% when hydrogen volume fraction were raised from 0% to 6.8%.

Investigation on performance of a spark-ignition engine fueled with dimethyl ether and gasoline mixtures under idle and stoichiometric conditions

This study investigated effects of dimethyl ether addition on the gasoline engine combustion and emissions performance under idle and stoichiometric conditions. The engine was first modified to be fueled with gasoline and dimethyl ether simultaneously. The experimental results showed that, with the increase of dimethyl ether energy fraction in the total fuel, the total fuel energy flow rate was decreased, and the flame development and propagation periods were shortened. The cycle-to-cycle variation was reduced and the degree of constant volume combustion was increased after the dimethyl ether addition. The dimethyl ether blending was beneficial for reducing hydrocarbon and nitrogen oxide emissions from 1951 and 95 ppm of the original engine to 552 and 34 ppm of pure dimethyl ether, respectively. Meanwhile, with the increase of dimethyl ether addition level, the peak cylinder pressure and carbon monoxide emission were decreased at first, whereas increased when the dimethyl ether energy fraction exceeded 49%. Furthermore, heat release rate during the low temperature reaction was enhanced with the increase of dimethyl ether addition level. The maximum heat release rate was heightened and its relevant crank angle was advanced during the high temperature reaction period after the dimethyl ether enrichment.

An experimental study of a hydrogen-enriched ethanol fueled Wankel rotary engine at ultra lean and full load conditions

In this paper, the effect of hydrogen addition to ethanol in a monorotor Wankel engine at wide open throttle position and in an ultra-lean operating regime was experimentally investigated. For this aim, variation of hydrogen enrichment levels on the ethanol engine performance and emissions were considered. Experiments were carried out under a constant engine speed of 3000rpm and fixed spark timing of 15 °BTDC. The test results showed that hydrogen enrichment improved the combustion process through shortening of the flame development and flame propagation periods and reducing the cyclic variation. Furthermore, the reduction of burn duration with the increase of hydrogen fraction enhances the thermal efficiency, reducing the brake-specific energy consumption, as well as reducing the unburned hydrocarbons emissions of the Wankel engine.

Effect of hydrogen addition on combustion and emissions performance of a gasoline rotary engine at part load and stoichiometric conditions

The rotary engines may encounter high fuel consumption and emissions due to its narrow and long combustion chamber design. The low ignition energy and high flame speed of hydrogen may help improve the combustion of rotary engines. In this paper, a gasoline rotary engine equipped with gasoline and hydrogen injectors was developed to investigate the combustion and emissions of hydrogen-blended gasoline rotary engines. The engine was run at 3000rpm and a manifolds absolute pressure of 37.5kPa with the stoichiometric excess air ratio. The spark timing was set to be 25°CA before the top dead center. The engine was first fueled with the pure gasoline and then blended with the hydrogen. The hydrogen volume fractions in the intake were gradually increased from 0% to 5.2%. The results showed that the combustion pressure, brake mean effective pressure, cylinder temperature and thermal efficiency were simultaneously increased after the hydrogen blending. The crank angle of peak pressure was advanced with the hydrogen addition. The hydrogen enrichment was effective on reducing flame development and propagation periods. HC emissions were reduced by 44.8% when the hydrogen volume fraction in the intake was raised from 0% to 5.2%, CO and CO2 emissions were also reduced after the hydrogen blending.