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Research Papers: Fuel Combustion

Analysis of Ignition Behavior in a Turbocharged Direct Injection Dual Fuel Engine Using Propane and Methane as Primary Fuels

[+] Author and Article Information
S. R. Krishnan

e-mail: krishnan@me.msstate.edu
Mississippi State University,
Starkville, MS 39762

1Corresponding author.

Contributed by the Internal Combustion Engine Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received March 9, 2012; final manuscript received January 3, 2013; published online May 24, 2013. Assoc. Editor: Gregory Jackson.

J. Energy Resour. Technol 135(3), 032202 (May 24, 2013) (10 pages) Paper No: JERT-12-1047; doi: 10.1115/1.4023482 History: Received March 09, 2012; Revised January 03, 2013

Dual fuel engine combustion utilizes a high-cetane fuel to initiate combustion of a low-cetane fuel. The performance and emissions benefits (low NOx and soot emissions) of dual fuel combustion are well-known. Ignition delay (ID) of the injected high-cetane fuel plays a critical role in quality of the dual fuel combustion process. This paper presents experimental analyses of the ID behavior for diesel-ignited propane and diesel-ignited methane dual fuel combustion. Two sets of experiments were performed at a constant engine speed (1800 rev/min) using a four-cylinder direct injection diesel engine with the stock electronic conversion unit (ECU) and a wastegated turbocharger. First, the effects of fuel–air equivalence ratios (Фpilot ∼ 0.2–0.6 and Фoverall ∼ 0.2–0.9) on IDs were quantified. Second, the effects of gaseous fuel percent energy substitution (PES) and brake mean effective pressure (BMEP) (from 2.5 to 10 bars) on IDs were investigated. With constant Фpilot (>0.5), increasing Фoverall with propane initially decreased ID but eventually led to premature propane auto-ignition; however, the corresponding effects with methane were relatively minor. Cyclic variations in the start of combustion (SOC) increased with increasing Фoverall (at constant Фpilot) more significantly for propane than for methane. With increasing PES at constant BMEP, the ID showed a nonlinear trend (initially increasing and later decreasing) at low BMEPs for propane but a linearly decreasing trend at high BMEPs. For methane, increasing PES only increased IDs at all BMEPs. At low BMEPs, increasing PES led to significantly higher cyclic SOC variations and SOC advancement for both propane and methane. Finally, the engine ignition delay (EID), defined as the separation between the start of injection (SOI) and the location of 50% of the cumulative heat release, was also shown to be a useful metric to understand the influence of ID on dual fuel combustion. Dual fuel ID is profoundly affected by the overall equivalence ratio, pilot fuel quantity, BMEP, and PES. At high equivalence ratios, IDs can be quite short, and beyond a certain limit, can lead to premature auto-igniton of the low-cetane fuel (especially for a reactive fuel like propane). Therefore, it is important to quantify dual fuel ID behavior over a range of engine operating conditions.

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Figures

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Fig. 1

Schematic of the experimental setup

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Fig. 2

Definitions of SOI, SOC, CA50 HR, ignition delay, and engine ignition delay

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Fig. 3

Ignition delay versus overall equivalence ratio for diesel-ignited propane combustion; BMEPs range from 1 bar to 12.9 bars; boost pressure held constant for each Фpilot value

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Fig. 4

Heat release, needle lift, and cylinder pressure profiles for one normal case (no propane auto-ignition) and two cases with propane auto-ignition as shown in Fig. 3

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Fig. 7

Ignition delay versus PES at BMEPs of 2.5, 5, 7.5, and 10 bars for diesel-ignited propane combustion. Boost pressure was maintained at 0% PES value for a given BMEP (1.18 bars, 1.28 bars, 1.40 bars, and 1.55 bars, respectively).

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Fig. 8

Cyclic variations in SOC for 2.5 bars BMEP and various PES of propane with constant boost pressure of 1.2 bars; standard deviations of SOC were 0.17, 0.24, 0.26, and 0.6 CAD for 0%, 25%, 50%, and 73% PES, respectively

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Fig. 5

Cyclic variations in SOC for Фpilot = 0.5 and various propane concentrations (Фoverall = 0.6, 0.7, and 0.8) with a constant boost pressure of 1.4 bars and BMEPs ranging from 7.2 to 11.2 bars; standard deviations of SOC were 0.16, 0.25, 0.6, and 0.4 CAD for Фoverall = 0.5, 0.6, 0.7, 0.8, respectively

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Fig. 6

Engine ignition delay versus overall equivalence ratio for diesel-ignited propane combustion; BMEPs 1 bar to 12.9 bars; boost pressure maintained at baseline Фpilot value

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Fig. 9

Ignition delay versus overall equivalence ratio for diesel-ignited methane combustion; BMEPs range from 1 bar to 12.9 bars; boost pressure held constant for each Фpilot value

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Fig. 10

Cyclic variations in SOC for Фpilot = 0.5 and various methane concentrations (Фoverall = 0.6, 0.7, 0.8, and 0.9) with a constant boost pressure of 1.4 bars and BMEPs ranging from 7.2 to 12.2 bars; standard deviations of SOC were 0.17, 0.17, 0.2, 0.19, and 0.19 CAD for Фoverall of 0.5, 0.6, 0.7, 0.8, and 0.9, respectively

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Fig. 11

Engine ignition delay versus overall equivalence ratio for diesel-ignited methane combustion; BMEPs 1 bar to 12.9 bars; boost pressure maintained at baseline Фpilot value

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Fig. 12

Ignition delay versus PES at BMEPs of 2.5, 5, 7.5, and 10 bars for diesel-ignited methane combustion. Boost pressure was maintained at 0% PES value for a given BMEP (1.18 bars, 1.28 bars, 1.40 bars, and 1.55 bars, respectively).

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Fig. 13

Cyclic variations in SOC for 2.5 bars BMEP and various PES of methane with constant boost pressure of 1.2 bars; standard deviations of SOC were 0.17, 0.16, 0.17, 0.51, and 0.63 CAD, respectively, for 0, 25, 50, 75, and 83% PES

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