What Limits Lean Operation in Spark Ignition Engines-Flame Initiation or Propagation?

Quader, Ather A.

doi:10.4271/760760

Cited by 137 publications

(32 citation statements)

References 13 publications

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“…If flames were ineffective and auto-ignition prevailed, the combustion continued to exhibit the baseline HCCI phasing ($8°after TDC) over the range of spark timings. This method differed from previous SI engine studies that relied on incomplete combustion or partial misfire to determine flame limits [8,15,21] and allowed for the investigation of flame behavior at ultra-dilute operating conditions.…”

Section: Methodsmentioning

confidence: 92%

“…While experience has shown that gasoline fueled spark ignited engines encounter a lean limit at approximately 30% dilution by mass [8], it is possible to sustain flames under higher levels of dilution provided the unburned gas temperature (T u ) is in the vicinity of the auto-ignition temperature and the energy content of the charge is sufficiently high [9]. For a given spark timing, as T u increases conditions become more favorable for auto-ignition and flame propagation tends to become an increasingly smaller percentage of the overall heat release [2].…”

Section: Introductionmentioning

confidence: 99%

“…Quader [8] performed experiments in a single cylinder engine with adjustable compression ratio to understand if flame initiation and/or flame propagation limited lean SI operation. In the experiments, spark timing was advanced earlier into compression and away from maximum brake torque (MBT) timing to define the ignition limit where the onset of misfire occurred.…”

Section: Introductionmentioning

confidence: 99%

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On the sensitivity of low temperature combustion to spark assist near flame limit conditions

Olesky

Middleton

Lavoie

et al. 2015

Fuel

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h i g h l i g h t sThe effect of spark assist on air and EGR dilute HCCI combustion was examined. Spark had greater combustion advance effect on more air dilute (vs. EGR dilute) mixtures. Combustion advance was caused by an increased fraction of flame-based heat release. Flame quenching likely affected mixtures that showed a non-response to spark assist. a b s t r a c t Spark assisted compression ignition (SACI) is a practical mode for controlling the heat release rate of low temperature combustion (LTC). While flames are key phenomena in the SACI combustion process, they may not always be effective or viable under the mildly stratified and highly dilute low burned gas temperature conditions of LTC. To better understand the limits of flammability or flame effectiveness, this work explores combustion within a single cylinder direct injection engine near the high load limit of the HCCI combustion regime, where spark induced flame propagation has been seen to affect combustion phasing and heat release rate. Flame limiting conditions were identified using progressively more advanced spark timing, up to 120°before top dead center, for differing levels of air and EGR dilution while holding the chemical energy content of the charge constant. Under air dilute conditions, the measured combustion phasing advanced from 8°to 0°after top dead center with spark advance, while almost no effect was seen under EGR dilute conditions. Estimates of the experimental global and local state conditions were made at the time of spark using heat release analysis and a KIVA-3V engine model, respectively, and the flammability for each case was evaluated using the Karlovitz criterion. The results show that fuel rich stratification near the spark plug was likely responsible for the observed variations in the SACI flame behavior.

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Section: Methodsmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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On the sensitivity of low temperature combustion to spark assist near flame limit conditions

Olesky

Middleton

Lavoie

et al. 2015

Fuel

View full text Add to dashboard Cite

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“…While spark retard increases the gas temperatures later in the engine cycle, addition of EGR reduces those temperatures and causes the fuel charge to burn more slowly. If the charge burns too slowly, it is possible that there will be occasional partial burns in which the exhaust valve will open prior to completion of combustion as suggested by Quader (1976) for lean limit combustion. This would, of course, result in an increase in exhaust hydrocarbon concentration.…”

Section: ) Spark Titnirigmentioning

confidence: 98%

The Effect of Fuel and Operating Variables on Hydrocarbon Species Distributions in the Exhaust from a Multicylinder Engine

Kaiser

Rothschild

Lavoie

1983

Combustion Science and Technology

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Measurements of the concentrations of individual exhaust hydrocarbon species have been made as a function of engine operating variables (a, rpm. EGR, spark timing, and coolant temperature) in a 2.3-liter four-cylinder engine. Three fuels were used i n these experiments: propane, isooctane (2.2,4-trimethylpentane), and an unleaded gasoline (indolene clear). The results show that a change in operating variable can change not only the total hydrocarbon concentration but also the distribution of species in the exhaust. All three fuels show similar trends when an operating variable is changed. Fuel-air equivalence ratio is a critical parameter i n controlling exhaust hydrocarbon emissions. Beginning near stoichiometric, the total hydrocarbon concentration and the percentage contributions of methane and acetylene to the exhaust increase as the mixture becomes richer. These species contribute less than 2 percent to the total hydrocarbon emissions at 0<0.95. Their contribution rises to 15-25 percent at 0=1.2 depending on the fuel used. The likely cause for this increase is incomplete combustion in the bulk gas o f the cylinder. These results highlight the importance o f chemical as well as physical effects in the production of hydrocarbon emissions during combustion. The exhaust hydrocarbon species distribution is also very sensitive lo the engine speed and spark timing in the absence of EGR.Increasing the engine speed or retarding the spark causes the hydrocarbon emissions to decrease. These parameters change principally the concentration of unburned fuel in the exhaust, while the concentrations of partial oxidation products remain approximately constant. Addition o f EGR increases all hydrocarbon concentrations and changes the dependence of hydrocarbon emission on spark timing. With an EGR rate equal to 213 of the maximum tolerance of the engine. the hydrocarbon emissions increase as the spark is retarded. This increase consists of increased concentrations of partial oxidation products in the exhaust gases, while the concentration of fuel remains unchanged.

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“…Burning natural gas (containing mostly methane) with air-fuel ratios larger than stoichiometric (lean conditions) in spark-ignited engines has the potential to produce lower emissions and higher thermal efficiencies than petroleum-burning engines [1,2]. However, if the air-fuel mixture is too lean, the high amount of air dilution destabilizes combustion, decreasing flame speeds and making the air-fuel mixture more difficult to ignite [3,4]. When combustion becomes unstable due to increased air dilution, engine performance and efficiency deteriorate, limiting the full potential of lean combustion.…”

Section: Introductionmentioning

confidence: 99%

Extending Lean Operating Limit and Reducing Emissions of Methane Spark-Ignited Engines Using a Microwave-Assisted Spark Plug

Rapp

DeFilippo

Saxena

et al. 2012

Journal of Combustion

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A microwave-assisted spark plug was used to extend the lean operating limit (lean limit) and reduce emissions of an engine burning methane-air. In-cylinder pressure data were collected at normalized air-fuel ratios of λ = 1.46, λ = 1.51, λ = 1.57, λ = 1.68, and λ = 1.75. For each λ, microwave energy (power supplied to the magnetron per engine cycle) was varied from 0 mJ (spark discharge alone) to 1600 mJ. At lean conditions, the results showed adding microwave energy to a standard spark plug discharge increased the number of complete combustion cycles, improving engine stability as compared to spark-only operation. Addition of microwave energy also increased the indicated thermal efficiency by 4% at λ = 1.68. At λ = 1.75, the spark discharge alone was unable to consistently ignite the air-fuel mixture, resulting in frequent misfires. Although microwave energy produced more consistent ignition than spark discharge alone at λ = 1.75, 59% of the cycles only partially burned. Overall, the microwave-assisted spark plug increased engine performance under lean operating conditions (λ = 1.68) but did not affect operation at conditions closer to stoichiometric.

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What Limits Lean Operation in Spark Ignition Engines-Flame Initiation or Propagation?

Cited by 137 publications

References 13 publications

On the sensitivity of low temperature combustion to spark assist near flame limit conditions

On the sensitivity of low temperature combustion to spark assist near flame limit conditions

The Effect of Fuel and Operating Variables on Hydrocarbon Species Distributions in the Exhaust from a Multicylinder Engine

Extending Lean Operating Limit and Reducing Emissions of Methane Spark-Ignited Engines Using a Microwave-Assisted Spark Plug

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