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The Ultra-Lean Partially Stratified Charge Approach to Reducing Emissions in Natural Gas Spark-Ignited Engines

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Natural Gas Engines

Part of the book series: Energy, Environment, and Sustainability ((ENENSU))

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Abstract

Lean-burn natural gas engines can be used to reduce exhaust emissions significantly. However, as the mixture is leaned out, the occurrence of extinction and incomplete combustion increases, resulting in poor performance and stability, as well as elevated levels of unburned hydrocarbon (UHC) and nitrogen oxides (NOx) emissions. The partially stratified charge (PSC) method can be used to mitigate these issues, while extending the lean misfire limit (LML) beyond its equivalent, homogeneous level. In this chapter, the PSC ignition and combustion processes are examined following a comprehensive experimental and numerical approach. Experiments are conducted in an idealized PSC configuration, using a constant volume combustion chamber (CVCC), to identify the principle enabling mechanisms of the PSC methodology. Engine tests conducted in a single-cylinder research engine (SCRE) demonstrate the feasibility of various PSC implementations in improving performance and emission characteristics in real-world settings. Complementary numerical analyses for the CVCC are obtained through large eddy simulations (LES), while Reynolds-averaged Navier–Stokes (RANS) simulations are conducted for SCRE with reduced chemical kinetics. The corresponding simulated results provide additional insights in characterizing the effect of fuel stratification on flame kernel maturation and flame propagation, the interplay between chemistry and turbulence at different overall air–fuel ratios, as well as formation of major pollutant species.

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Abbreviations

D o :

Injector nozzle diameter (mm)

E :

Energy (kJ)

f :

Arbitrary function

H :

Energy content of air–fuel mixture (kJ)

k :

Turbulent kinetic energy (m2/s2)

K e :

Jet entrainment constant (–)

L e :

Turbulent integral length scale (mm)

m e :

Entrained jet mass (mg)

m fuel :

Mass of fuel (in air–fuel mixture) (mg)

m o :

Injected jet mass (mg)

p :

Pressure (bar)

p :

Power in Lp combination (–)

S L :

Laminar flame speed (m/s)

t :

Time (s)

t 0 :

Time at start of injection (s)

T :

Temperature (K)

uʹ:

Turbulent velocity fluctuation (m/s)

U o :

Jet velocity at nozzle (m/s)

V :

Volume (cc)

z :

Jet penetration distance (mm)

Z :

Normalized energy release (–)

γ :

Ratio of specific heats (–)

Γ:

Jet penetration constant (–)

δL:

Laminar flame brush thickness (m)

ε :

Dissipation rate of turbulent kinetic energy (m2/s3)

ϕ :

Fuel–air ratio relative to stoichiometric level (–)

λ :

Air–fuel ratio relative to stoichiometric level (–)

μ :

Mean value of an observable

μ j :

Mixing ratio between entrained and injected mass (–)

ρ ∞ :

Density of ambient gas (kg/m3)

ρ 0 :

Density of injected gas (kg/m3)

ρ b :

Density of burned gas (kg/m3)

ρ u :

Density of unburned gas (kg/m3)

σ :

Standard deviation of an observable

τ :

Normalized time (–)

abs:

Absolute (pressure level)

AMR:

Adaptive mesh refinement

AS:

After spark onset

ASOI:

After start of injection (ms)

BFSC:

Brake-specific fuel consumption (g/kWh)

BMEP:

Brake-specific mean effective pressure (bar)

B/ATDC:

Before/after top dead center

CAD:

Crank angle degree (°)

CFD:

Computational fluid dynamics

(C)NG:

(Compressed) natural gas

CoV:

Coefficient of variation (%)

CVCC:

Constant volume combustion chamber

DNS:

Direct numerical simulation

HR(R):

Heat release (Rate) (kJ (/s))

I/EVC:

Intake/exhaust valve closed

I/EVO:

Intake/exhaust valve open

IMEP:

Indicated mean effective pressure (bar)

LES:

Large eddy simulation

LML:

Lean misfire limit (–)

LPG:

Liquefied petroleum gas

MBT:

Mean best torque

MFB:

Mass fraction burned (%)

NOx:

Nitrogen oxides (i.e., NO + NO2)

PaSR:

Partially stirred reactor

PM:

Particulate matter

PSC:

Partially stratified charge

RANS:

Reynolds-averaged Navier–Stokes

RNG:

Renormalization group

RPM:

Revolutions per minute

S/EOI:

Start/end of injection (ms)

SCRE:

Single-cylinder research engine

T/BDC:

Top/bottom dead center

TCI:

Turbulence chemistry interaction

TKE:

Turbulent kinetic energy (m2/s2)

(U)HC:

(Unburned) hydrocarbon

WOT:

Wide-open throttle

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Authors and Affiliations

  1. Department of Industrial Engineering, University of Rome “Tor Vergata”, Rome, Italy

    L. Bartolucci, S. Cordiner & V. Mulone

  2. Institute for Advanced Sustainability Studies, Potsdam, Germany

    E. C. Chan

  3. Department of Mechanical Engineering, The University of British Columbia, Vancouver, BC, Canada

    R. L. Evans

Authors
  1. L. Bartolucci
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  2. E. C. Chan
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  3. S. Cordiner
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  4. R. L. Evans
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  5. V. Mulone
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Corresponding authors

Correspondence to L. Bartolucci or E. C. Chan .

Editor information

Editors and Affiliations

  1. Department of Mechanical Engineering, The University of Alabama, Tuscaloosa, AL, USA

    Kalyan Kumar Srinivasan

  2. Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh, India

    Avinash Kumar Agarwal

  3. Department of Mechanical Engineering, The University of Alabama, Tuscaloosa, AL, USA

    Sundar Rajan Krishnan

  4. Department of Industrial Engineering, University of Rome Tor Vergata, Rome, Italy

    Vincenzo Mulone

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Bartolucci, L., Chan, E.C., Cordiner, S., Evans, R.L., Mulone, V. (2019). The Ultra-Lean Partially Stratified Charge Approach to Reducing Emissions in Natural Gas Spark-Ignited Engines. In: Srinivasan, K., Agarwal, A., Krishnan, S., Mulone, V. (eds) Natural Gas Engines . Energy, Environment, and Sustainability. Springer, Singapore. https://doi.org/10.1007/978-981-13-3307-1_3

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  • DOI: https://doi.org/10.1007/978-981-13-3307-1_3

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