Conditional Analysis of Enhanced Combustion Luminosity Imaging in a Spray-Guided Gasoline Engine with High Residual Fraction

Zeng, Wei; Idicheria, Cherian A.; Fansler, Todd D.; Drake, Michael C.

doi:10.4271/2011-01-1281

Cited by 17 publications

(10 citation statements)

References 11 publications

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“…All cycles in the dashed rectangle shown in Figure 6(b) are used to produce probability maps to indicate the likelihood of flame location (shown in Figure 8), following the approach discussed in a previous study. 30 The threshold value is chosen to be 100 out of a total image intensity depth of 4095. This threshold is based on empirical observation and makes the probability maps reflect the statistical location of both the weaker blue flame along with the higher intensity regions.…”

Section: And 5)mentioning

confidence: 99%

Utilizing boost and double injections for enhanced stratified-charge direct-injection spark-ignition engine operation with gasoline and E30 fuels

Zeng

Sjöberg

2017

International Journal of Engine Research

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This study systematically explores the effects of injection strategy and exhaust-gas recirculation on boosted stratifiedcharge operation of a direct-injection spark-ignition engine using gasoline and E30 fuels at absolute intake pressures in the range of 100-160 kPa. Nitrogen dilution is used to lower the intake mole fraction of oxygen to simulate the dilution effects of exhaust-gas recirculation. The engine is operated at 1000 r/min with an gross indicated mean effective pressure range of 380-680 kPa. In summary, significant reductions of engine-out NO x and soot emissions can be achieved for stratified operation while still maintaining stable combustion (~2% gross indicated mean effective pressure variability) and high thermal efficiency (~40%). Adding exhaust-gas recirculation significantly suppresses NO x emissions, not only by reducing flame temperatures but also by slowing down the combustion which effectively retards the combustion phasing. A well-designed closely spaced double-injection strategy is key to combustion stabilization and plays an important role to suppress soot emissions. Intake boost allows reaching higher loads with further reduced soot emissions. High-speed dual-camera flame imaging reveals key features of flame propagation for stratified operation with low NO x emissions at high exhaust-gas recirculation levels. Heat release rate-based conditional analysis of flame images shows that compared to single injection, the use of double injections creates a spark plasma that is more stretched out, correlating with a more stable early combustion. It also demonstrates that double injections produce more symmetric flame propagation with smaller soot-containing regions, indicating more favorable fuel distributions. Stratified operation with gasoline and E30 fuels demonstrates similar engine performance and emission levels for double injections. These observations suggest that E0 (gasoline)-E30 fuel blends can be compatible with highly efficient stratified-charge spark-ignited operation. However, for a 50/50 double-injection strategy, E30 showed elevated smoke emissions for operation without intake boost, indicating that certain operating strategies can be adversely affected by the ethanol content of E30 fuel blends.

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Section: And 5)mentioning

confidence: 99%

Utilizing boost and double injections for enhanced stratified-charge direct-injection spark-ignition engine operation with gasoline and E30 fuels

Zeng

Sjöberg

2017

International Journal of Engine Research

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“…The probability maps are created by using a 10% peak intensity threshold to binarize the individual cycle flames following the method in Ref. [13,14]. (The smoother contours observed in the OH* images are partly due to the filtering applied to the more granular images acquired with the lower-spatial resolution intensified camera.…”

Section: Natural Flame-luminosity Imagingmentioning

confidence: 99%

“…There is also a trade-off between operation favorable to low soot and that favorable to low NO x . High levels of residuals or EGR are used to minimize NO x emissions [13] but increase exhaust particulates and reduce combustion stability. The deterioration of combustion stability with EGR can be especially pronounced at higher engine speeds, where the magnitude of the flow variability can be higher [14].…”

Section: Introductionmentioning

confidence: 99%

The role of spray-enhanced swirl flow for combustion stabilization in a stratified-charge DISI engine

Zeng¹,

Sjöberg²,

Reuss³

et al. 2016

Combustion and Flame

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Implementation of spray-guided stratified-charge direct-injection spark-ignited (DISI) engines is inhibited by the occurrence of misfire and partial burns. Engine-performance tests demonstrate that increasing engine speed induces combustion instability, but this deterioration can be prevented by generating swirling flow during the intake stroke. In-cylinder pressure-based heat-release analysis reveals that the appearance of poor-burn cycles is not solely dependent on the variability of early flame-kernel growth. Cycles can experience burning-rate regression during later combustion stages and may or may not recover before the end of the cycle. Thermodynamic analysis and optical diagnostics are used here to clarify why swirl improves the combustion repeatability from cycle to cycle.The fluid dynamics of swirl/spray interaction was previously demonstrated using high-speed PIV measurements of in-cylinder motored flow. It was found that the sprays of the multi-hole injector redistribute the intake-generated swirl flow momentum, thereby creating a better-centered higher angularmomentum vortex with reduced variability. The engine operation with high swirl was found to have significant improvement in cycle-to-cycle variations of both flow pattern and flow momentum. This paper is an extension of the previous work. Here, PIV measurements and flame imaging are applied to fired operation for studying how the swirl flow affects variability of ignition and subsequent combustion phases. PIV results for fired operation are consistent with the measurements made of motored flow. They demonstrate that the spark-plasma motion is highly correlated with the direction of the gas flow in the vicinity of the spark-plug gap. Without swirl, the plasma is randomly stretched towards either side of the spark plug, causing variability in the ignition of the two spray plumes that are straddling the spark plug. In contrast, swirl flow always convects the spark plasma towards one spray plume, causing a more repeatable ignition. The swirl decreases local RMS velocity, consistent with an observed reduction of early-burn variability. Broadband flame imaging demonstrates that with swirl, the flame consistently propagates in multiple directions to consume fuel-air mixtures within the piston bowl. In contrast, operation without swirl displays higher variability of flame-spread patterns, occasionally causing the appearance of partial-burn cycles.

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“…25 For operation with gasoline, there may be a trade-off between soot and NO x (nitrogen oxides) emissions, similar to that of traditional diesel engines. 26 High levels of residuals or exhaust-gas recirculation (EGR) can be used to minimize NO x emissions 27 but tend to increase exhaust particulates. On the contrary, high-level ethanol blends can be used to suppress soot formation and simultaneously achieve low NO x and particulate matter (PM).…”

Section: Introductionmentioning

confidence: 99%

The use of partial fuel stratification to enable stable ultra-lean deflagration-based Spark-Ignition engine operation with controlled end-gas autoignition of gasoline and E85

Zhang

Sjöberg

et al. 2019

International Journal of Engine Research

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Lean operation of Spark-Ignition engines can provide higher thermal efficiency compared to standard stoichiometric operation. However, for a homogeneous lean mixture, the associated reduction of flame speeds becomes an important issue from the perspective of robust ignition and fast flame spread throughout the charge. This study is focused on the use of a lean partial fuel stratification strategy that can stabilize the deflagration, while sufficiently fast combustion is ensured via the use of end-gas autoignition. The engine has a spray-guided Direct-Injection Spark-Ignition combustion system and was fueled with either a high-octane certification gasoline or E85. Partial fuel stratification was achieved using several fuel injections during the intake stroke in combination with a small pilot-injection concurrent with the Spark-Ignition. The results reveal that partial fuel stratification enables very stable combustion, offering higher thermal efficiency for parts of the load range in comparison to well-mixed lean and stoichiometric combustion. The heat release and flame imaging demonstrate that the combustion often has three distinct stages. The combustion of the pilot-injected fuel, ignited by the normal spark, acts as a “super igniter,” ensuring a very repeatable initiation of combustion, and flame incandescence reveals locally rich conditions. The second stage is mainly composed of blue flame propagation in a well-mixed lean mixture. The third stage is the compression autoignition of a well-mixed and typically very lean end-gas. The end-gas autoignition is critical for achieving high combustion efficiency, high thermal efficiency, and stable combustion. Partial fuel stratification enables very effective combustion-phasing control, which is critical for controlling the occurrence and intensity of end-gas autoignition. Comparing the gasoline and E85 fuels, it is noted that achieving end-gas autoignition for the higher octane E85 requires a more aggressive compression of the end-gas via the use of a more advanced combustion phasing or higher intake-air temperature.

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Conditional Analysis of Enhanced Combustion Luminosity Imaging in a Spray-Guided Gasoline Engine with High Residual Fraction

Cited by 17 publications

References 11 publications

Utilizing boost and double injections for enhanced stratified-charge direct-injection spark-ignition engine operation with gasoline and E30 fuels

Utilizing boost and double injections for enhanced stratified-charge direct-injection spark-ignition engine operation with gasoline and E30 fuels

The role of spray-enhanced swirl flow for combustion stabilization in a stratified-charge DISI engine

The use of partial fuel stratification to enable stable ultra-lean deflagration-based Spark-Ignition engine operation with controlled end-gas autoignition of gasoline and E85

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