Dependence of premixed low-temperature diesel combustion on fuel ignitability and volatility

Abstract

Abstract:A comprehensive study of fuel property effects in internal combustion engines is required to enable fuel diversification as well as applications to advanced engines being developed for operation with a variety of combustion modes. The objective of this paper is to investigate the effects of fuel ignitability and volatility over a wide range on premixed low-temperature combustion (LTC) modes in diesel engines. Twenty three fuels were prepared from commercial gasoline, kerosene, and diesel as baseline fuels and with the addition of additives, to generate a cetane number (CN) range from 11 to 75. Experiments with a single cylinder diesel engine operated in moderately-advanced-injection LTC modes were conducted to evaluate these fuels. The combustion phasing is demonstrated to be a good indicator to estimate the in-cylinder peak pressure, exhaust gas emissions, and thermal efficiency in the LTC mode. Fuel ignitability affects the combustion phasing by changing the ignition delay. The predicted cetane number (PCN) based on fuel molecular structure analysis can be fitted to the ignition delays with a higher coefficient of determination than CN, suggesting a good potential as a fuel ignitability measure over a wide range. The stable operating load range in the smokeless LTC mode depends more on the actual ignition delay or PCN rather than CN. With fixed injection timing and intake oxygen concentration, O 2in , only when PCN < 40, the load range can be expanded significantly to higher loads. With holding the combustion phasing at TDC and varying O 2in , the NOx and smoke emissions become limitations of the load expansion for some fuels. The effects of fuel volatility on the characteristics of LTC are small compared to ignitability. Finally, the operational injection timing range and robustness of the LTC to fuel ignitability are examined, showing that the advantageous ignitability range becomes narrower with fuel ignitability decreasing.

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

“…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].…”

“…The rapid increases in population and living standards in developing countries are expected to increase global demand for transportation energy at an annual rate of 1 -1.5% through at least 2050 [1][2][3][4]. Despite strong growth in alternative energy, traditional petroleum-based fuels (gasoline, diesel and jet fuel) are expected to dominate the transportation energy portfolio, both for light-and heavy-duty applications [2][3][4]. In addition, there is ample evidence that sufficient crude reserves exist to meet this increased demand [4,5].…”

Direct injection of neat n-butanol for enabling clean low temperature combustion in a modern diesel engine

“…EGR ratios) can be effective to enable LTC for simultaneous reduction of NO x and particulate emissions, as reported in [22][23][24][25][26][27][28][29][30][31][32]. In terms of fuel properties, empirical results suggested that less ignitable fuels could assist to extend the LTC operation to higher engine loads, while the impact of fuel volatility was relatively minor [33][34][35][36]. In comparison to the majority of diesel fuels, n-butanol has a lower Cetane number ($25) and an oxygen content of 22% by weight.…”

Experimental study on the two stage injection of diesel and gasoline blends on a common rail injection system

“…premixed low temperature combustion (LTC) have been extensively studied, accomplishing simultaneous reduction in NOx and soot emissions with deteriorated thermal efficiency [1,2]. Fuel properties are crucial for the combustion process and emissions formation in the advanced engine combustion strategies [3,4]. The optimized fuel properties are proved to promote uniform mixture formation, which could restrict the in-cylinder soot-favorable region and avoid heavy usage of exhaust gas recirculation, as employed in the conventional LTC mode, to reduce combustion temperature below the soot formation threshold.…”