Effects of In-Cylinder Mixing on Low Octane Gasoline Compression Ignition Combustion

Abstract

Gasoline compression ignition (GCI) engines have been considered an attractive alternative to traditional spark ignition engines. Low octane gasoline fuel has been identified as a viable option for the GCI engine applications due to its longer ignition delay characteristics compared to diesel and in the volatility range of gasoline fuels. In this study, we have investigated the effect of different injection timings at part-load conditions using light naphtha stream in single cylinder engine experiments in the GCI combustion mode with injection pressure of 130 bar. A toluene primary reference fuel (TPRF) was used as a surrogate for the light naphtha in the engine simulations performed here. A physical surrogate based on the evaporation characteristics of the light naphtha has been developed and its properties have been implemented in the engine simulations. Full cycle GCI computational fluid dynamics (CFD) engine simulations have been successfully performed while changing the start of injection (SOI) timing from -50° to -11 ° CAD aTDC. The effect of SOI on mixing and combustion phasing was investigated using detailed equivalence ratio-temperature maps and ignition delay times. Both experimental and computational results consistently showed that an SOI of -30° CAD aTDC has the most advanced combustion phasing (CA50), with the highest NOx emission. The effects of the SOI on the fuel containment in the bowl of the piston, the ignition delay time, combustion rate and emissions have been carefully examined through the CFD calculations. It was found that the competition between the equivalence ratio and temperature is the controlling parameter in determining the combustion phasings.

Optimization of the octane response of gasoline/ethanol blends

“…The development of the blending rule starts with PRF and TPRF mixtures with ethanol, since these are widely used surrogates for gasoline fuels [44,[71][72][73][74][75][76]. Also, establishing an octane number regression model for PRFs/ethanol and TPRFs/ethanol blends would significantly aid the efforts in designing modern engines fuels with optimum ON response due to the addition of ethanol.…”

Autoignition of straight-run naphtha: A promising fuel for advanced compression ignition engines

“…technologies that combine the best of gasoline and diesel engines. Combustion strategies such as homogeneous charge compression ignition (HCCI) [6], reactivity-controlled compression ignition (RCCI) [7][8][9], and partially-premixed compression ignition (PPCI) [10][11][12][13] have sought to combine the relatively simple design of gasoline engines and their after treatment systems and the higher efficiencies of diesel engines benefits. These engine technologies share some high-level characteristics even though the engine operating parameters such as timing and number of injections, fuel type, and air system requirements may differ.…”

“…Many fuels with varying physical and chemical properties, such as ignition quality, distillation curve and chemical compositions, have been considered in previous works. These include conventional gasoline [3,[14][15][16][17][18], conventional diesel [11,14,[17][18][19][20][21][22], gasoline-diesel blends ("dieseline") [3,21,[23][24][25], low-octane gasolines ("naphthas") [3,10,12,[14][15][16]26] and reference fuel blends (composed of iso-octane, n-heptane, toluene) [3,14,16,27,28]. Certain fuel properties could affect the performance of the engine because PPCI combustion is dependent on mixture stratification as well as chemical kinetics [29] .For example, some studies indicate that there are direct impacts of fuel distillation and aromatic content on the soot emissions of PPCI engines [21,30], while others report a minimal effect [31].…”

“…Studying PRF and TPRF surrogates provide guidance on the conditions (temperatures, pressures and equivalence ratios) under which such simple surrogates may be utilized to mimic the ignition properties of a complex real fuel such as HSRN. This is useful for performing computational fluid dynamic (CFD) simulations, which must use widely available reduced chemical kinetic mechanisms [12,13,35].…”

Ignition delay measurements of a low-octane gasoline blend, designed for gasoline compression ignition (GCI) engines

“…Combustion strategies such as homogeneous charge compression ignition (HCCI) [3], reactivity-controlled compression ignition (RCCI) [4][5][6], and partially-premixed compression ignition (PPCI) [7][8][9][10] have sought to combine the benefits of relatively simple design of gasoline engines and their after-treatment systems and the higher efficiencies of diesel engines. The compression ignition combustion mode eliminates traditional engine knock observed in spark-ignition (SI) engines, and removes throttling losses through direct injection (DI).…”