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

  • L. Bartolucci
  • E. C. Chan
  • S. Cordiner
  • R. L. Evans
  • V. Mulone
Part of the Energy, Environment, and Sustainability book series (ENENSU)


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.


Natural gas combustion Spark ignition (SI) engine Lean combustion Stratified charge High efficiency Low emissions 

Roman Symbols


Injector nozzle diameter (mm)


Energy (kJ)


Arbitrary function


Energy content of air–fuel mixture (kJ)


Turbulent kinetic energy (m2/s2)


Jet entrainment constant (–)


Turbulent integral length scale (mm)


Entrained jet mass (mg)


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


Injected jet mass (mg)


Pressure (bar)


Power in Lp combination (–)


Laminar flame speed (m/s)


Time (s)


Time at start of injection (s)


Temperature (K)


Turbulent velocity fluctuation (m/s)


Jet velocity at nozzle (m/s)


Volume (cc)


Jet penetration distance (mm)


Normalized energy release (–)

Greek Symbols


Ratio of specific heats (–)


Jet penetration constant (–)


Laminar flame brush thickness (m)


Dissipation rate of turbulent kinetic energy (m2/s3)


Fuel–air ratio relative to stoichiometric level (–)


Air–fuel ratio relative to stoichiometric level (–)


Mean value of an observable


Mixing ratio between entrained and injected mass (–)


Density of ambient gas (kg/m3)


Density of injected gas (kg/m3)


Density of burned gas (kg/m3)


Density of unburned gas (kg/m3)


Standard deviation of an observable


Normalized time (–)

Acronyms and Abbreviations


Absolute (pressure level)


Adaptive mesh refinement


After spark onset


After start of injection (ms)


Brake-specific fuel consumption (g/kWh)


Brake-specific mean effective pressure (bar)


Before/after top dead center


Crank angle degree (°)


Computational fluid dynamics


(Compressed) natural gas


Coefficient of variation (%)


Constant volume combustion chamber


Direct numerical simulation


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


Intake/exhaust valve closed


Intake/exhaust valve open


Indicated mean effective pressure (bar)


Large eddy simulation


Lean misfire limit (–)


Liquefied petroleum gas


Mean best torque


Mass fraction burned (%)


Nitrogen oxides (i.e., NO + NO2)


Partially stirred reactor


Particulate matter


Partially stratified charge


Reynolds-averaged Navier–Stokes


Renormalization group


Revolutions per minute


Start/end of injection (ms)


Single-cylinder research engine


Top/bottom dead center


Turbulence chemistry interaction


Turbulent kinetic energy (m2/s2)


(Unburned) hydrocarbon


Wide-open throttle


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Copyright information

© Springer Nature Singapore Pte Ltd. 2019

Authors and Affiliations

  1. 1.Department of Industrial EngineeringUniversity of Rome “Tor Vergata”RomeItaly
  2. 2.Institute for Advanced Sustainability StudiesPotsdamGermany
  3. 3.Department of Mechanical EngineeringThe University of British ColumbiaVancouverCanada

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