Author ORCID Identifier

https://orcid.org/0000-0001-7483-6650

Semester

Summer

Date of Graduation

2023

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Dr. Cosmin Dumitrescu

Committee Member

Dr. Derek Johnson

Committee Member

Dr. John Hu

Committee Member

Dr. V'yachelslav Akkerman

Committee Member

Dr. Mahdi Darzi

Abstract

As natural gas production infrastructure is already in place in most of the world and will continue expanding for the foreseeable future, natural gas is an alternative to traditional liquid petroleum fuels in heavy-duty engines. Dedicated natural gas or dual-fuel diesel-natural gas heavy-duty engines are alternatives to diesel-only power generation equipment. One challenge is the large variation in the natural gas composition available for such applications, which is known to significantly affect engine’s combustion characteristics and the emissions composition. As the literature on dual-fuel combustion under low load engine operating conditions that use more realistic natural gas mixtures (i.e., mixtures that, in addition of methane (C1;the most abundant natural gas component), also contain ethane (C2), propane (C3), and butane (C4)) is limited, this study evaluated the combustion characteristics of a variety of C1-C4 mixtures using three different experimental platforms: a 4.5-L 4-cylinder heavy-duty production diesel engine modified for dual-fuel diesel-natural gas engine operation, a prototype 1.125-L single-cylinder engine with extended optical access that was based on the same production diesel engine, and a laminar flame burner.

Experiments in the heavy-duty production engine under low load dual-fuel diesel-natural gas operating conditions (6 bar break mean effective pressure at 1000 RPM, 1000 bar diesel injection pressure, and 40% diesel substitution ratio) showed that gas composition affected the diesel fuel ignition delay and combustion phasing, which are known to affect both engine performance and emissions. As in-cylinder pressure correlated with the autoignition temperature of the gaseous mixture, mixtures with higher C2-C4 content produced the best engine performance and emissions compared to using 100% C1, suggesting that the addition of C2-C4 content benefits low load dual-fuel combustion. For example, brake specific carbon dioxide and nitrogen oxides emissions reduced up to 6.6% and 20%, respectively. In addition, gas mixtures containing C3 and C4 reduced the brake specific carbon dioxide equivalent by up to 50 g/kWh compared to the C1-only case.

Experiments in the prototype single cylinder optical engine employed imaging diagnostics to better understand the C1-C4 effects observed in the production engine experiments. High boost and high intake temperature were used to create in-cylinder conditions similar to those in the production engine at the start of combustion. To enhance the visual differences between the natural gas components, only one component was used at a time instead of a multicomponent mixture as in the production engine experiments, and difficulties in accurately controlling the C4 flow resulted in using only C1-C3. Experiments were performed at similar low load dual fuel operating conditions (~ 6.6 bar indicated mean effective pressure at 1000 RPM, 500 bar diesel injection pressure, and ~ 63% diesel substitution ratio), using both traditional and advanced diesel injection timing (i.e., conventional mixing-controlled compression ignition or MCCI compared to reactivity-controlled compression ignition or RCCI). Natural luminosity data showed that C3 RCCI had a more advanced combustion phasing despite an increased ignition delay and higher spatially-integrated natural luminosity compared to C1 RCCI and C2 RCCI. An earlier premixed combustion and a smaller phasing difference between the apparent heat release and spatially-integrated natural luminosity was seen for MCCI compared to RCCI. The results suggested that the C1-C3 content indeed affected the diesel gas mixing and stratification of the low load dual-fuel operation, hence the differences in engine performance and emissions observed in the production engine experiments. As a result, the findings in this study can be used for modeling the dual-fuel combustion of C1-C4 blends and can help industry in utilizing more efficiently natural gas with higher C2-C4 content.

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