Experimental Investigation of Water Injection in a Stoichiometric Dual-Fuel NG-Diesel Engine at Medium and High Loads

Document Type

Conference Proceeding

Publication Date

1-8-2026

Department

Visual and Performing Arts; Department of Mechanical and Aerospace Engineering

Abstract

Dual-fuel diesel–natural gas engines have emerged as a promising alternative to conventional engines due to natural gas’s lower cost, wide availability, high ignition energy due to the diesel pilot, and potential for reducing CO2 emissions with diesel-like efficiency. However, dual-fuel engines operating at medium and high loads still face challenges, including combustion knock and high NOx emissions. Water injection is a strategy to mitigate these issues. This study experimentally evaluates the impact of port water injection on the combustion characteristics, performance, and emissions of a stoichiometric natural gas-diesel pilot engine. A six-cylinder, turbocharged, direct-injection diesel engine with a 17.3:1 compression ratio was modified to operate on 85% natural gas and 15% diesel energy, with diesel as the ignition source. Tests were conducted at engine speeds of 1800 rpm, and brake mean effective pressures (BMEP) of 12.5 and 16.8 bar, with water-to-fuel ratios (WFR) ranging from 0 to 2.5 in increments of 0.5. 12.5 bar BMEP was chosen to align with modern stationary power applications of 126 kW and the 16.8 bar BMEP load to evaluate the impact of water injection at full load. The results show that increasing the WFR leads to a reduction in NOx emissions and combustion knock. Specifically, pre-ignition observed at 16.8 bar BMEP was mitigated with a WFR of 0.5:1. At 12.5 bar BMEP, NOx emissions were reduced by 45% with a WFR of 1.5:1. Additionally, particulate matter concentration decreased with increasing WFR. With a WFR of 2.5:1 at 16.8 bar BMEP, particulate matter levels were reduced by a factor of 3.5, but incurred a reduction in brake thermal efficiency from 42% to 40%. Overall, experiments showed that port water injection can be used as a combustion control strategy in a stoichiometric NG diesel pilot engine to decrease NOx, knock, particulate matter, and mitigate pre-ignition, all while maintaining diesel-like efficiency and combustion stability.

Publication Title

International Combustion Engine Division Fall Technical Conference

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