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

Abstract

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.

Combustion development in a gasoline-fueled spark ignition–controlled auto-ignition engine operated at different spark timings and intake air temperatures

“…In the case of 498 and 523 K, it is seen that advancing ST has little effect on mean IMEP values and combustion timing of CA50. 20 In addition, the variations in CA50 increase considerably with advancing ST. Compared with the effect of Tintake at the same ST, increasing Tintake reduced IMEP values as increasing Tintake causes the amount of incoming charge to be decreased due to decreasing its density.…”

“…19 SICAI combustion under highly diluted mixture can, therefore, result in the engine cycles in which misfire or partial-burn occurs due to flammability limit. 20 Lavoie et al 21 presented the multi-mode combustion diagram depending on the temperature of burned and unburned zones in the cylinder for SI, SICAI, and pure CAI operating regions restricted with the boundaries of flame, NOx, and knocking limits. A schematic diagram illustrating the boundaries of spark-assisted HCCI categorized into three ranges is also given by Wang et al 22 They defined the regions with the status of temperature and the concentration of the mixture in the cylinder.…”

Investigation into ethanol effects on combustion and particle number emissions in a spark-ignition to compression-ignition (SICI) engine

“…Spark assistance is an effective method to improve combustion stability and extend engine load of homogeneous charge compression ignition (HCCI) [1][2][3][4][5][6], which has been applied in Mazda J o u r n a l P r e -p r o o f SKYACTIV-X [7] and can be further combined with vehicle electrification in near future. From the viewpoint of transportation energy, blending oxygenated components with conventional hydrocarbon fuels is beneficial to green-house gas (GHG) and particulate emission reduction while co-optimization of engines and oxygenated fuel is required [8].…”

“…Among the aforementioned methods, spark assistance along with fuel stratification has a relatively low cost and only requires one fuel supply system, which has the potential to be applied in the combustion modes involving controlled auto-ignition, such as spark-ignition to compression-ignition (SICI) mode, in the near future. SICI combustion has been substantially studied in engines and fundamental research devices, e.g., rapid compression machines (RCM), using pure high-RON gasolines [1][2][3][4][5][6][26][27][28][29], ethanol-gasoline blends [24,31] and their surrogate fuels [32][33][34][35][36][37] in the past decade. Specifically, Wang et al [1] achieved SICI combustion at medium-high loads using commercial 93# gasoline and external exhaust gas recirculation (EGR), an indicated specific fuel consumption (ISFC) less than 225 g/kW•h was obtained at about 22% EGR.…”

“…Specifically, Wang et al [1] achieved SICI combustion at medium-high loads using commercial 93# gasoline and external exhaust gas recirculation (EGR), an indicated specific fuel consumption (ISFC) less than 225 g/kW•h was obtained at about 22% EGR. Olesky et al [3,5,26] investigated the influence of intake temperature, spark advance for flame limit extension and diluent composition on heat release ratio rate using RON 87 gasoline provided by Chevron Phillips. The results showed that the advanced spark timing could compensate for the decrease in intake temperature.…”