Experimental Studies of Low-Load Limit in a Stoichiometric Micro-Pilot Diesel Natural Gas Engine

Vinicius Bonfochi Vinhaes, Gordon McTaggart-Cowan, Sandeep Munshi, Mahdi Shahbakhti and Jeffrey D. Naber
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Vinicius Bonfochi Vinhaes: Mechanical Engineering-Engineering Mechanics, Michigan Technological University, Houghton, MI 49931, USA
Gordon McTaggart-Cowan: School of Sustainable Energy Engineering, Faculty of Applied Sciences, Simon Fraser University, Surrey, BC V3T 0N1, Canada
Sandeep Munshi: Advanced Engineering, Westport Fuel Systems Inc., Vancouver, BC V6P 6G2, Canada
Mahdi Shahbakhti: Mechanical Engineering Department, University of Alberta, Edmonton, AB T6G 2R3, Canada
Jeffrey D. Naber: Mechanical Engineering-Engineering Mechanics, Michigan Technological University, Houghton, MI 49931, USA

Energies, 2022, vol. 15, issue 3, 1-18

Abstract: While operating at light loads, diesel pilot-ignited natural gas engines with lean premixed natural gas suffer from poor combustion efficiency and high methane emissions. This work investigates the limits of low-load operation for a micro-pilot diesel natural gas engine that uses a stoichiometric mixture to enable methane and nitrogen oxide emission control. By optimizing engine hardware, operating conditions, and injection strategies, this study focused on defining the lowest achievable load while maintaining a stoichiometric equivalence ratio and with acceptable combustion stability. A multi-cylinder diesel 6.7 L engine was converted to run natural gas premix with a maximum diesel micro-pilot contribution of 10%. With a base diesel compression ratio of 17.3:1, the intake manifold pressure limit was 80 kPa(absolute). At a reduced compression ratio of 15:1, this limit increased to 85 kPa, raising the minimum stable load. Retarding the combustion phasing, typically used in spark-ignition engines to achieve lower loads, was also tested but found to be limited by degraded diesel ignition at later timings. Reducing the pilot injection pressure improved combustion stability, as did increasing pilot quantity at the cost of lower substitution ratios. The lean operation further reduced load but increased NOx and hydrocarbon emissions. At loads below the practical dual-fuel limit, a transition to lean diesel operation will likely be required with corresponding implications for the aftertreatment system.

Keywords: high-efficiency engine; micro-pilot diesel; natural gas; stoichiometric operation; low load (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2022
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