Study on Combustion and Emissions of a Combined Injection Spark Ignition Engine with Natural Gas Direct Injection...

Area of Science:

• Internal Combustion Engines
• Alternative Fuels
• Combustion Science

Background:

• Conventional ethanol spark ignition (SI) engines suffer from poor fuel atomization and mixture formation.
• Lean-burn conditions in SI engines present challenges for combustion efficiency and emissions control.

Purpose of the Study:

• To improve combustion and emission performance of ethanol SI engines under lean-burn conditions.
• To investigate the effects of dual-injection mode combining ethanol port injection (EPI) and compressed natural gas direct injection (CDI).

Main Methods:

• Engine performance testing at 1500 rpm.
• Systematic variation of compressed natural gas direct injection ratios (CDIr) and excess air ratios (λ).
• Analysis of key performance indicators including torque, pressure, emissions, and combustion duration.

Main Results:

• Increasing CDIr under lean-burn conditions reduces CO, HC emissions, and improves stability (CoV_IMEP).
• Optimal combination of 15% CDI and 85% EPI with λ = 1.1 enhances torque, peak pressure (Pmax), and combustion duration (CA 10-90).
• The dual-injection strategy significantly expands the lean-burn limit (λ up to 1.73) and reduces harmful emissions.

Conclusions:

• Dual-injection of CNG and ethanol in SI engines creates a stratified mixture, boosting power and stability.
• The 15% CDI + 85% EPI combination at λ = 1.1 offers a superior solution for natural gas/ethanol SI engines.
• This approach effectively addresses the limitations of conventional ethanol SI engines under lean-burn operation.