Determining the optimum fuel concentration for ignition and combustion of semi-coke and bituminous coal blends with rich/lean burner

Dual-fuel (DF) engines offer great fuel flexibility combined with low emissions in gas mode. The main source of energy in this mode is provided by gaseous fuel, while the diesel fuel acts only as an ignition source. For this reason, the reliable autoignition of the pilot fuel is of utmost importance for combustion in DF engines. However, the autoignition of the pilot fuel suffers from low compression temperatures caused by Miller valve timings. These valve timings are applied to increase efficiency and reduce nitrogen oxide (NOx) emissions. Previous studies have investigated the influence of injection parameters and operating conditions on ignition and combustion in DF engines using a unique periodically chargeable combustion cell. Direct light high-speed images and pressure traces clearly revealed the effects of injection parameters and operating conditions on ignition and combustion. However, these measurement techniques are only capable of observing processes after ignition. In order to overcome this drawback, a high-speed shadowgraph technique was applied in this study to examine the processes prior to ignition. Measurements were conducted to investigate the influence of compression temperature and injection pressure on spray formation and ignition. Results showed that the autoignition of diesel pilot fuel strongly depends on the fuel concentration within the spray. The high-speed shadowgraph images revealed that in the case of very low fuel concentration within the pilot spray, only the first stage of the two-stage ignition occurs. This leads to large cycle-to-cycle variations and misfiring. However, it was found that a reduced number of injection holes counteract these effects. The comparison of a diesel injector with ten-holes and a modified injector with five-holes showed shorter ignition delays, more stable ignition and a higher number of ignited sprays on a percentage basis for the five-hole nozzle.

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Experimental Study on Characteristics of Pyrolysis, Ignition and Combustion of Blends of Petroleum Coke and Coal in CFB

18th International Conference on Fluidized Bed Combustion ◽

10.1115/fbc2005-78048 ◽

2005 ◽

Cited By ~ 2

Author(s):

Changsui Zhao ◽

Chuanmin Chen ◽

Xiaoping Chen ◽

Fengjun Wang ◽

Wenxuan Wang ◽

...

Keyword(s):

Partial Pressure ◽

Petroleum Coke ◽

Ignition Temperature ◽

Bituminous Coal ◽

Molar Ratio ◽

Flow Ratio ◽

Co2 Partial Pressure ◽

Mechanism Model ◽

Ignition And Combustion ◽

Mass Flow Ratio

It is a common understanding that co-firing of petroleum coke and coal in circulating fluidized bed (CFB) is an efficient, economical and environment-friendly way to utilize petroleum coke with medium or high sulfur content. Experimental investigations on characteristics of pyrolysis, ignition and combustion of petroleum coke, coal and their blends with different mixing ratios were conducted on a thermogravimetric analyzer and a pilot CFB combustor systematically. Ignition temperature and burnout temperature were also acquired. The effects of several parameters in terms of the fuel category, the heating rate, the coal/coke mass flow ratio, the CO2 partial pressure, and the Ca/S molar ratio on the ignition and burnout characteristics of the petroleum coke and the blends of the petroleum coke and coal were verified. The results show that the ignition temperature and the burnout temperature of the petroleum coke are between those of bituminous coal and anthracite, which implies that its combustion characteristic is between bituminous coal and anthracite, but is more closer to the bituminous. The pyrolysis process of blends of petroleum coke and coal accords with mechanism model (1−α)1.5 well, and the combustion process accords with mechanism model w1.5 well. Although the ignition temperature of the blended fuels keeps the same when the heating rate, or the CO2 partial pressure or the Ca/S molar ratio increases, the burnout temperature decreases gradually. With decrease in the coal/coke mass flow ratio, the ignition temperature and the burnout temperature of the blends rise.

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Local fuel concentration, ignition and combustion in a stratified charge spark combustion in a stratified charge spark ignited direct injection engine: Spectroscopic, imaging and pressure-based measurements

International Journal of Engine Research ◽

10.1243/146808703321533240 ◽

2003 ◽

Vol 4 (2) ◽

pp. 61-86 ◽

Cited By ~ 28

Author(s):

T. D. Fansler ◽

M. C. Drake ◽

B Stojkovic ◽

M. E. Rosalik

Keyword(s):

High Speed ◽

Equivalence Ratio ◽

Direct Injection ◽

Injection Timing ◽

Cylinder Pressure ◽

Engine Operation ◽

Stratified Charge ◽

Fuel Concentration ◽

Spark Gap ◽

Ignition And Combustion

A recently developed spark emission spec-troscopy technique has been used to measure the effects of fuel injection timing, spark timing and intake swirl level on the individual-cycle fuel concentration at the spark gap in a wall-guided spark ignited direct injection (SIDI) engine. The fuel-concentration measurements were made simultaneously with measurements of individual-cycle spark discharge energy and cylinder pressure. Endoscopic imaging of the fuel spray and high-speed imaging of combustion (both broadband and spectrally resolved) augment these quantitative data. For optimum engine operation, the fuel-air equivalence ratio at the spark gap just after spark breakdown is rich on average (〈φ〉 ≈1.4–1.5) and varies widely from cycle to cycle (∼25 per cent). The evolution with crank angle of the mean equivalence ratio and its cycle-to-cycle fluctuations are correlated with the cylinder pressure, heat release and imaging data to provide insights into fuel transport and mixture preparation that are important to understanding and optimizing ignition and combustion in SIDI engines. For example, causes of misfires and partial burns have been determined.

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Ignition of Diesel Pilot Fuel in Dual-Fuel Engines

Volume 1: Large Bore Engines; Fuels; Advanced Combustion ◽

10.1115/icef2018-9671 ◽

2018 ◽

Author(s):

Marcus Grochowina ◽

Daniel Hertel ◽

Simon Tartsch ◽

Thomas Sattelmayer

Keyword(s):

High Speed ◽

Measurement Techniques ◽

Injection Pressure ◽

Operating Conditions ◽

Dual Fuel ◽

Spray Formation ◽

Fuel Concentration ◽

Injection Parameters ◽

Pilot Fuel ◽

Ignition And Combustion

Dual-Fuel (DF) engines offer great fuel flexibility combined with low emissions in gas mode. The main source of energy in this mode is provided by gaseous fuel, while the Diesel fuel acts only as an ignition source. For this reason, the reliable autoignition of the pilot fuel is of utmost importance for combustion in DF-engines. However, the autoignition of the pilot fuel suffers from low compression temperatures caused by Miller valve timings. These valve timings are applied to increase efficiency and reduce nitrogen oxide emissions. Previous studies have investigated the influence of injection parameters and operating conditions on ignition and combustion in DF-engines using a unique periodically chargeable combustion cell. Direct light high-speed images and pressure traces clearly revealed the effects of injection parameters and operating conditions on ignition and combustion. However, these measurement techniques are only capable of observing processes after ignition. In order to overcome this drawback, a high-speed shadowgraph technique was applied in this study to examine the processes prior to ignition. Measurements were conducted to investigate the influence of compression temperature and injection pressure on spray formation and ignition. Results showed that the autoignition of Diesel pilot fuel strongly depends on the fuel concentration within the spray. The high-speed shadowgraph images revealed that in the case of very low fuel concentration within the pilot spray only the first-stage of the two-stage ignition occurs. This leads to large cycle-to-cycle variations and misfiring. However, it was found that a reduced number of injection holes counteracts these effects. The comparison of a Diesel injector with 10-holes and a modified injector with 5-holes showed shorter ignition delays, more stable ignition and a higher number of ignited sprays on a percentage basis for the 5-hole nozzle.

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