The effects of split injections on high exhaust gas recirculation low-temperature diesel engine combustion

Proceedings of the Institution of Mechanical Engineers, Part D:

McTaggart-Cowan

et al. 2012

Self Cite

This paper shows that a split-fuel-injection strategy can achieve robust, near-zero smoke and nitrogen oxide emissions at reduced exhaust gas recirculation levels under low-temperature combustion conditions. The overall objective of the work was to investigate the sensitivity (in terms of the engine emissions and the fuel economy) of a 50:50 (by mass) split-injection strategy to variations in the key engine operating parameters. Experiments were performed at operating conditions corresponding to a gross indicated mean effective pressure of 500 kPa at an engine speed of 1500 r/min in a 0.51 l single-cylinder high-speed direct-injection diesel engine. The paper presents the effects of different relative fuel injection timings at a variable intake oxygen mass fraction (10.5% and 12%) at a constant intake pressure (120 kPa, absolute) on the smoke, total hydrocarbon and carbon monoxide emissions with the split-main-injection strategy. The effects of a variable fuel injection pressure (90 MPa and 110 MPa) on diesel low-temperature combustion with split injection are also reported, as are the effect of an increased intake pressure (150 kPa, absolute). The combined effects of the operating parameters and the fuel injection timing on the smoke, nitrogen oxide, total hydrocarbon and carbon monoxide emissions and the gross indicated specific fuel consumption are described. For selected operating conditions, the cycle-resolved spray and combustion processes are visualized together with the flame temperature measurement using two-colour optical pyrometry to understand the combustion phenomena occurring in the split-injection strategy. The results of the optical studies show that different low-temperature combustion operating conditions producing similarly low levels of ‘engine-out’ smoke emissions have substantially different histories of soot formation and soot oxidation. An increase in the intake oxygen mass fraction reduced the total hydrocarbon emissions and the gross indicated specific fuel consumption at a given intake pressure, while a higher intake pressure reduced them further. Although significant soot formation took place from the second injection event, the majority of the soot was subsequently oxidized because of a slightly higher flame temperature and slightly higher oxygen concentration than in single-injection high-exhaust-gas-recirculation low-temperature combustion. A higher injection pressure did not have any significant effect on the emissions and the gross indicated specific fuel consumption.

Section: Introductionmentioning

confidence: 71%

Effects of engine operating parameters on diesel low-temperature combustion with split fuel injection

Sarangi

Proceedings of the Institution of Mechanical Engineers, Part D:

McTaggart-Cowan

et al. 2012

Self Cite

“…As a consequence of the reduced flame temperature and lower in-cylinder oxygen concentrations found in LTC, it is usual for the emissions of unburned total hydrocarbons (THC) and carbon monoxide (CO) emissions to increase significantly. This effect has been demonstrated for a wide range of different LTC strategies including homogeneous charge compression ignition LTC [4,5], moderate EGR split injection LTC [6,7], single injection high-EGR LTC/partially premixed compression ignition LTC [8,9,10,11,12], premixed charge compression ignition LTC [13,14] and reactivity controlled compression ignition LTC [15,16]. Less homogeneous charge distribution, including locally fuel-lean and fuel-rich regimes, leads to a more stratified combustion process in high-EGR LTC compared to homogeneous charge approaches.…”

Section: Introductionmentioning

confidence: 88%

The impact of intake pressure on high exhaust gas recirculation low-temperature compression ignition engine combustion using borescopic imaging

Sarangi

International Journal of Engine Research

McTaggart-Cowan

et al. 2020

In diesel engines, high levels of exhaust gas recirculation can be used to achieve low-temperature combustion, resulting in low emission levels of both nitrogen oxides (NO x) and particulate matter. This work studied the effects of varying the intake manifold pressure on in-cylinder combustion processes and engine-out emissions from a light-duty single cylinder diesel engine under conventional and high exhaust gas recirculation low-temperature combustion regimes. The work was conducted at a part-load cruise condition of 1500 r/min and at an indicated mean effective pressure of approximately 600 kPa. Exhaust gas recirculation rates were varied between 0% and 65% at absolute intake pressures of 100–150 kPa. Very low NO x emissions were achieved (<10 ppm, ∼0.05 g/kW h) for intake oxygen mass fractions below about 11%, independent of boost pressure. Smoke emission levels were lower than for non–exhaust gas recirculation combustion at oxygen mass fractions below ∼9%, depending on the boost pressure. High intake pressures reduced fuel consumption by 15% and combustion by-product emissions by 50%–60% compared to low boost. For the low intake boost case, little visible flame was apparent through borescope imaging. At higher boost pressures, intense flame luminosity was observed within the piston bowl early in the expansion stroke. Spatially averaged soot luminosity based on photomultiplier tube data showed that peak soot luminosity was five times greater and occurred 8 °CA earlier for high boost. This work demonstrates how the combination of appropriate boost pressures and exhaust gas recirculation rates can be used to mitigate the emissions and thermal efficiency penalties of high-dilution low-temperature combustion to achieve near-zero NO x operation.

“…The research engine facility, which has been fully described and illustrated schematically in a number of previous works from the authors' research group, [7][8][9][10][11] was instrumented with the provision to measure boosted intake air temperature and pressure, fuel and air flow rates, and in-cylinder pressure. Intake pressure was measured using Kistler 4045A5 piezo-resistive pressure transducer while the in-cylinder pressure was measured with a piezoelectric AVL QC34C flushmounted water-cooled transducer.…”

Section: Experimental Set-upmentioning

confidence: 99%

Effects of intake-port throttling on combustion behaviour in diesel low-temperature combustion

Sogbesan

International Journal of Engine Research

Davy

2017

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Citation: SOGBESAN AbstractThis paper describes the effects of intake-port throttling on diesel low temperature combustion (LTC) at a low and medium load condition. These conditions were known for their characteristically high hydrocarbon (HC) emissions predominantly from over-mixed and under-mixed mixture zones respectively. The investigation was carried out to supplement current findings in literature with valuable information on the formation of HC emissions with increasing swirl levels generated by intake-port throttling. This was achieved through the use of cycle-resolved HC measurements in addition to cycle averaged emissions and in-cylinder pressure-derived metrics. While there was negligible overall effect at the moderately-dilute lowload conditions, increasing swirl has been shown to be beneficial to premixing efficacy under highly dilute conditions with extended ignition delay. This potential advantage was found to be nullified by the swirlinduced confinement of fuel and combustion products to the central region of the cylinder leading to poor late cycle burn rates and increased smoke emissions. HC emissions from the squish and head quench regions were reduced by an increase in swirl ratio.