Diesel-like efficiency using CNG/diesel dual-fuel combustion

Karthik Nithyanandan, Jiaxiang Zhang, Yuqiang Li, Xiangyu Meng, Robert Donahue, Chia Fon F. Lee, Huili Dou

Research output: Chapter in Book/Report/Conference proceedingConference contribution


The use of natural gas in compression ignition engines as a supplement to diesel under dual-fuel combustion mode is a promising technique to increase efficiency and reduce emissions. In this study, the effect of dual-fuel operating mode on combustion characteristics, engine performance and pollutant emissions of a diesel engine using natural gas as primary fuel and neat diesel as pilot fuel, has been examined. Natural Gas (99% Methane) was port injected into an AVL 5402 single cylinder diesel research engine under various engine operating conditions and up to 90% substitution was achieved. In addition, neat diesel was also tested as a baseline for comparison. The experiments were conducted at three different speeds - 1200, 1500 and 2000 RPM, and at different diesel-equivalent loads (injection quantity) - 15, 20, and 25 mg/cycle. Both performance and emissions data are presented and discussed. The performance was evaluated through measurements of in-cylinder pressure, power output and various exhaust emissions including unburned hydrocarbons (UHC), carbon monoxide (CO), nitrogen oxides (NOx) and soot. The goal of these experiments was to maximize the efficiency. This was done as follows - the CNG substitution rate (based on energy) was increased from 30% to 90% at fixed engine conditions, to identify the optimum CNG substitution rate. Then using that rate, a main injection timing sweep was performed. Under these optimized conditions, combustion behavior was also compared between single, double and triple injections. Finally, a load and speed sweep at the optimum CNG rate and timings were performed. It was found that a 70 % CNG substitution provided the highest indicated thermal efficiency. It appears that dual-fuel combustion has a Maximum Brake Torque (MBT) diesel injection timing for different conditions which provides the highest torque. Based on multiple diesel injection tests, it was found that the conditions that favor pure diesel combustion, also favor dual-fuel combustion because better diesel combustion provides better ignition and combustion for the CNG-air mixture. For 70% CNG dual-fuel combustion, multiple diesel injection showed an increase in the efficiency. Based on the experiments conducted, diesel-CNG dual-fuel combustion is able to achieve similar efficiency and reduced emissions relative to pure diesel combustion. As such, CNG can be effectively used to substitute for diesel fuel in CI engines.

Original languageEnglish (US)
Title of host publicationLarge Bore Engines; Fuels; Advanced Combustion
PublisherAmerican Society of Mechanical Engineers
ISBN (Electronic)9780791857274
StatePublished - Jan 1 2015
EventASME 2015 Internal Combustion Engine Division Fall Technical Conference, ICEF 2015 - Houston, United States
Duration: Nov 8 2015Nov 11 2015

Publication series

NameASME 2015 Internal Combustion Engine Division Fall Technical Conference, ICEF 2015


OtherASME 2015 Internal Combustion Engine Division Fall Technical Conference, ICEF 2015
Country/TerritoryUnited States

ASJC Scopus subject areas

  • Automotive Engineering
  • Mechanical Engineering
  • Fuel Technology


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