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Insight into the Effect of Excess Air Coefficient on a Methanol/Diesel RCCI Engine under Various Altitudes
Yiyuan Peng1, Fenlian Huang1, Mingding Wan1
1Yunnan Key Laboratory of Internal Combustion Engines, Kunming University of Science and Technology, 650500 Kunming, China.
ACS Omega
|March 30, 2026
Summary
Optimizing methanol-diesel RCCI combustion with excess air coefficient (λ) and altitude significantly reduces total hydrocarbon (THC) emissions. However, excessively lean conditions or high altitudes can increase NOx, soot, and particulate matter.
Area of Science:
- Internal Combustion Engines
- Sustainable Energy Technologies
- Environmental Science
Background:
- Methanol/diesel Reactivity Controlled Compression Ignition (RCCI) combustion offers high efficiency and low emissions for diesel engines.
- Carbon neutrality targets necessitate advanced combustion strategies for sustainable transportation.
- Understanding the impact of operating parameters like excess air coefficient (λ) and altitude is crucial for real-world application.
Purpose of the Study:
- To experimentally investigate the coupled effects of excess air coefficient (λ) and altitude on combustion characteristics and emissions in a methanol-diesel RCCI engine.
- To analyze performance under low and medium operating conditions relevant to practical diesel engine use.
- To provide data for optimizing MD-RCCI engine calibration across diverse environmental conditions.
Main Methods:
- Experimental investigation of a methanol-diesel RCCI engine.
- Varying excess air coefficient (λ) from lean to rich conditions.
- Testing across an altitude range of 0-2000 meters under low (1400 rpm-25% load) and medium (1800 rpm-50% load) operating points.
Main Results:
- Decreasing λ significantly reduces total hydrocarbon (THC) emissions, with reductions up to 68.7% at medium load.
- Increasing altitude generally leads to longer ignition delay, decreased peak pressure and heat release rate, but increased peak temperatures and exhaust gas temperatures.
- High altitude and excessively low λ increase NOx, soot, and particulate number (PN) emissions, while CO emissions show load-dependent responses.
Conclusions:
- Optimizing λ is effective in reducing THC emissions in MD-RCCI engines, but requires careful consideration to avoid increased NOx, soot, and PN.
- Altitude significantly impacts combustion phasing, emissions, and efficiency, necessitating adaptive engine control strategies.
- The study provides crucial quantitative data for calibrating MD-RCCI engines for reliable and efficient operation in varying altitude environments.
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