Date of Award


Document Type

Open Access Master's Thesis

Degree Name

Master of Science in Mechanical Engineering (MS)

Administrative Home Department

Department of Mechanical Engineering-Engineering Mechanics

Advisor 1

Jeffery Naber

Advisor 2

Jeremy Worm

Committee Member 1

Brian Eggart

Committee Member 2

Scott Miers


Natural gas has been gaining popularity as an alternative fuel due to its high availability, low CO2 emissions, and low cost. In this experimental study, water injection’s impact on medium and heavy-duty engine operation fueled by natural gas and pilot diesel injection for ignition was studied under stochiometric operation for use with a three-way catalytic converter to meet criteria emissions for off-road power generation. To retain high efficiencies, a high compression ratio of 17.3:1 was used. Maintaining stoichiometric operation with a high compression ratio leads to combustion knock, pre-ignition, and high NOx formation. Conventionally, cooled EGR can be used to reduce NOx, but results in increased soot and does not eliminate combustion knock and pre-ignition. As an alternative to EGR this work utilized port injected water to provide on demand charge cooling, successfully reducing both NOx and soot while enabling high-load operation. A combination of both high and low speeds and loads were tested to study the impact of water injection on the emissions and performance of the natural gas, diesel-pilot engine. Additionally, water injections impact on diesel only operation was tested to provide comparison metrics and aid in a better understanding of the mechanisms at work when injecting water in an internal combustion engine.

At full load, 16.8 bar BMEP, it was found that a water to fuel ratio of 0.5:1 was sufficient to enabling the knock free operation without significant increase in combustion duration or instability where operating at this load without water resulted in pre-ignition. Increasing the water to fuel ratio to 1:1 enabled a 21 bar BMEP load. At 12.5 bar BMEP, the NOx emission was reduced from 13.5 g/kwh to 7.2 g/kwh with a water to fuel mass ratio of 1.5:1. In addition to solving the high NOx and pre-ignition problem, a water to fuel ratio of 2.5:1 at 16.8 bar BMEP also decreased the soot content in the exhaust by a factor of 3.5 with only a small penalty in efficiency, decreasing break thermal efficiency from 41 to 40%.