Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

Combustion Characteristics of Lean Burn and Stoichiometric With Exhaust Gas Recirculation Spark-Ignited Natural Gas Engines

[+] Author and Article Information
Hui Xu

Cummins, Inc.,
1900 McKinley Avenue,
Mail Code 50114,
Columbus, IN 47201
e-mail: hui.xu@cummins.com

Leon A. LaPointe

Cummins, Inc.,
1900 McKinley Avenue,
Mail Code 50114,
Columbus, IN 47201
e-mail: leon.a.lapointe@cummins.com

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received March 12, 2015; final manuscript received April 21, 2015; published online May 27, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(11), 111511 (Nov 01, 2015) (8 pages) Paper No: GTP-15-1090; doi: 10.1115/1.4030500 History: Received March 12, 2015; Revised April 21, 2015; Online May 27, 2015

Natural gas (NG) has been widely used in reciprocating engines for various applications such as automobile, electricity generation, and gas compression. It is in the public interest to burn fuels more efficiently and at lower exhaust emissions. NG is very suitable to serve this purpose due to its clean combustion, small carbon footprint, and, with recent breakthroughs in drilling technologies, increased availability and low cost. NG can be used in lean burn spark-ignited (LBSI) or stoichiometric EGR spark-ignited (SESI) engines. Selection of either LBSI or SESI requires accommodation of requirements such as power output/density, engine efficiency, emissions, knock margin, and cost. The work described in this paper investigated the feasibility of operating an engine originally built as an LBSI under SESI conditions. Analytical tools and workflow developed by Cummins, Inc., are used in this study. The tools require fundamental combustion properties as inputs, including laminar flame speed (LFS), adiabatic flame temperature (AFT), and auto-ignition interval (AI). These parameters provide critical information about combustion duration, engine out NOx, and relative knock propensity. An existing LBSI engine operating at its as released lambda was selected as baseline. The amount of exhaust gas recirculation (EGR) for the SESI configuration was selected so that it would have the same combustion duration as that of the LBSI at its reference lambda. One-dimensional (1D) cycle simulations were conducted under both SESI and LBSI conditions assuming constant output power, compression ratio, volumetric efficiency, heat release centroid, and brake mean effective pressure (BMEP). The 1D cycle simulations provide peak cylinder pressure (PCP) and peak unburned zone temperature (PUZT) under LBSI and SESI conditions. The results show that the SESI configuration has lower PCP but higher PUZT than that of the LBSI for the same output power. Also, for the same combustion duration, SESI has higher AFT than that of LBSI, resulting in higher engine out NOx emissions. The SESI configuration has shorter AI than that of LBSI engine, or smaller relative knock margin. Reduction of output power and emissions aftertreatment in the form of a three-way catalyst (TWC) is required to operate under SESI engine conditions.

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Fig. 1

Reference condition normalized cylinder pressure and heat release, spark timing = −24.80 ATDC

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Fig. 2

Normalized LFS at 60 bar, 900 K, 0% RH; NG, reference lambda 1.75

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Fig. 8

Normalized AFT at 60 bar, 900 K, lambda from 0.8 to 2.5 with 0% RH

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Fig. 3

Normalized cylinder pressure at various spark timing values; lambda = 1.75, reference condition PCP at spark timing = −24.80 ATDC

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Fig. 9

Measured BSNOx correlates well with AFT

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Fig. 4

Normalized unburned zone temperature at various spark timing values; lambda = 1.75, reference condition PUZT spark timing = −24.80 ATDC

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Fig. 5

Normalized cumulative heat release at various spark timing values, lambda = 1.75

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Fig. 6

Normalized PCP, PUZT, LFS, and heat release centroid at various spark timing values. Solid lines are linear regressions of the data.

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Fig. 7

Experimentally measured combustion duration at 1200 rpm correlates well with LFS

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Fig. 11

Normalized MKI correlates well with AI

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Fig. 12

Work flow to investigate feasibility of operating engines original built as LBSI under SESI conditions

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Fig. 10

End gas auto-ignition causing engine knock [6]

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Fig. 13

Normalized LFS for candidate LBSI and SESI conditions at 60 bar and 900 K

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Fig. 14

Normalized LFS computed at 60 bar and 900 K as a function of lambda; EGR levels under SESI conditions to provide equal LFS are shown attached to dotted lines; impact on observed normalized combustion duration is shown on right-hand scale

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Fig. 15

Normalized PCP for candidate LBSI and SESI conditions

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Fig. 16

Normalized PUZT for LBSI and SESI conditions

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Fig. 17

Normalized AFT for candidate LBSI and SESI conditions

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Fig. 18

Normalized AI for LBSI and SESI conditions

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Fig. 19

Normalized BTE for LBSI and SESI conditions

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Fig. 21

Bandpass filtered signal of the cylinder pressure trace

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Fig. 20

Cylinder pressure trace of a knocking engine cycle



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