Flame Propagation Durations Research Articles

Experimental Investigation of Combustion Characteristics of a Spark Ignition Engine Fueled with Methanol-Gasoline Blends (M15 and M85)

Combustion characteristics of a 2.8 kW, constant speed, spark ignition engine fuelled with methanol-gasoline blends (M15 and M85) were studied. It was observed that the maximum in-cylinder pressure and maximum heat release rate with M85 were almost like gasoline while these values were significantly lower with M15. The flame development duration was 30.5% and 5.5% shorter at lower and higher load respectively with M85 as compared to gasoline. In addition to this, the flame propagation duration was shorter by 37% and 14.28% at lower and higher load with M85. Similar results were obtained with M15 blend. The crank angle for fifty percent mass burnt fraction was near to the top dead centre of engine with both the blends as compared to gasoline. The methanol-gasoline fuelled spark ignition engine’s important combustion characteristics including heat release rate, cumulative heat release, combustion duration, flame development, propagation and laminar flame velocity are analysed in detail.

Relationship of flame propagation and combustion mode transition of end-gas based on pressure wave in confined space

The main objective of this work is to identify the end-gas combustion mode transition under different initial thermodynamic conditions and to focus on the role of pressure waves in autoignition formation and detonation development in the confined space by a group of two-dimensional (2D) numerical simulations with detailed chemistry of H2/air mixture. Pressure waves with different strengths are obtained by the flame acceleration in closed chambers with and without obstacles under three different initial temperatures. The results indicate that with the increase of initial temperature, there exist three different end-gas autoignition transition modes: autoignition promoted by strong flame acceleration, autoignition suppressed by weak flame acceleration and autoignition independent of flame acceleration. It is also shown that there are three types of end-gas autoignition-induced detonation initiation: (1) detonation initiated directly by the pressure wave generated from the flame propagation; (2) detonation initiated directly by the pressure wave generated from other hot-spot autoignition; (3) autoignition to detonation transition based on the reactivity gradient theory. Meanwhile, to further identify the autoignition transition mode under continuous variation of pressure wave intensity and initial temperature, an idealized physical model, with the Mach number of the pressure wave as the link between the flame propagation duration and autoignition time of the end-gas, is proposed. It is shown that the autoignition can be suppressed by the elevated flame speed when the pressure wave is weak, while it cannot be prevented intrinsically when the temperature of the end-gas is high or the pressure wave is strong enough. Moreover, different autoignition propagation modes are identified from Bradley's diagram, including deflagration, developing detonation and thermal explosion, and the combined effects of reactivity and pressure wave strength are discussed as well.

Combustion, performance and emission characteristics of fusel oil in a spark ignition engine

Alcohol based fuels attract the attention of alternative fuel researchers. Many studies have been performed about combustion, performance and emission characteristics of alcohol used in internal combustion engines. Fusel oil is an alcohol based fuel obtained as a by-product during alcohol fermentation. Up to the present there has been no study regarding the combustion characteristics of fusel oil in a spark ignition engine. In this experimental study, performance, emission and combustion characteristics of fusel oil were examined in a spark ignition engine at 2500rpm and four different engine loads. In-cylinder pressures, heat release rates, flame development and flame propagation durations, crank angles corresponding 50% of total mass fraction burnt, engine torque, brake specific fuel consumptions, CO, HC and NOx emissions were investigated. The water content and lower heating value of the fusel oil aggravated the combustion. Flame development and flame propagation durations were prolonged. As a result engine performance dropped. In addition, fusel oil usage increased CO and HC emissions up to 21% and 25% respectively. NOx emissions decreased about 31% due to worse combustion performance of fusel oil.

Performance and emission characteristics of a turbocharged spark-ignition hydrogen-enriched compressed natural gas engine under wide open throttle operating conditions

This paper investigates the effect of various hydrogen ratios in HCNG (hydrogen-enriched compressed natural gas) fuels on performance and emission characteristics at wide open throttle operating conditions using a turbocharged spark-ignition natural gas engine. The experimental data was taken at hydrogen fractions of 0%, 30% and 55% by volume and was conducted under different excess air ratio ( λ) at MBT operating conditions. It is found that under various λ, the addition of hydrogen can significantly reduce CO, CH 4 emissions and the NO x emission remain at an acceptable level when ignition timing is optimized. Using the same excess air ratio, as more hydrogen is added the power, exhaust temperatures and max cylinder pressure decrease slowly until the mixture’s lower heating value remains unchanged with the hydrogen enrichment, then they rise gradually. In addition, the early flame development period and the flame propagation duration are both shorter, and the indicated thermal efficiency and maximum heat release rate both increase with more hydrogen addition.

Study on combustion behaviors and cycle-by-cycle variations in a turbocharged lean burn natural gas S.I. engine with hydrogen enrichment

Lean burn is widely accepted as an effective approach to simultaneously improve spark-ignition engine's thermal efficiency and decrease exhaust emissions. But although lean burn has a lot of advantages it is also associated with several difficulties including slower flame propagation speed and increased cycle-by-cycle variations. Hydrogen addition is thought to be an ideal approach to tackle these problems. This paper presents an experimental work aimed at investigating the effects of hydrogen addition on the combustion behaviors and cycle-by-cycle variations in a turbocharged lean burn natural gas SI engine. The experiments were conducted over a wide range of hydrogen enhancement levels, equivalence ratios, spark timings, manifold absolute pressures and engine speeds. It is also found that hydrogen addition contributes much more to reducing flame development duration, whose reduction has greatly positive effects on keeping down cycle-by-cycle variations than to reducing flame propagation duration. Based on these combustion results, the effects of hydrogen addition on cycle-by-cycle variations at spark timings, various equivalence ratios, MAPs, engine speeds were also examined and it is concluded that cycle-by-cycle variations, which is of high importance in lean burn SI engines can indeed be lowered by hydrogen addition. Engine thermal efficiency and exhaust emissions were also investigated during the experiments. It is found that after hydrogen addition the engine's thermal efficiency could keep at relatively high level over a much wider range of equivalence ratios. When fixed at MBT spark timing, NO x emission also can be reduced by hydrogen addition.

Effects of hydrogen addition on cycle-by-cycle variations in a lean burn natural gas spark-ignition engine

An experimental study aimed at examining the effects of hydrogen addition on cycle-by-cycle variation (CCV) in an SI engine was conducted on a 6-cylinder throttle body injection natural gas (NG) engine. Two types of fuels, CNG and 80/20 (in volume) CNG/hydrogen mixtures, were used for comparison purposes. The results showed that coefficient of variation (CoV) in both maximum pressure ( P max ) and indicated mean effective pressure (IMEP) could be reduced by hydrogen addition and that positive effect would be more obvious as the engine was further leaned out. The duration of flame development and propagation as well as the CCVs in flame propagation duration could be simultaneously reduced by hydrogen addition, all of which are beneficial to improve combustion stability and thought to be reasons for the reduction in CoV imep . Stability of combustion phasing that is crucial to the effectiveness of ignition timing optimization was also improved by hydrogen. Hydrogen addition was also proved to be good to the control of emission of NO x and unburned HC. Hence it is concluded that hydrogen addition is an effective and applicable approach to keep down CCVs in lean burn spark-ignition engines.