THE EFFECTS OF HYDROGEN ADDITION AND INTAKE-INDUCED SWIRL ON THE CHARACTERISTICS OF NATURAL GAS COMBUSTION IN A SINGLE-CYLINDER SPARK-IGNITED ENGINE
Open Access
- Author:
- Corrigan, Melanie Kae
- Graduate Program:
- Fuel Science
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 17, 2011
- Committee Members:
- Andre Louis Boehman, Dissertation Advisor/Co-Advisor
Andre Louis Boehman, Committee Member
Alan W Scaroni, Committee Member
Sarma V Pisupati, Committee Member
Thomas Litzinger, Committee Member
Daniel Connell Haworth, Committee Member - Keywords:
- HCNG
combustion
CNG
turbulence
Hydrogen
burn duration - Abstract:
- Compressed natural gas (CNG) is an alternative fuel of interest for internal combustion engines (ICEs) in the mass transit and vocational applications. Increasingly, due to the abundant supply of shale gas, there is interest in heavy duty and in passenger vehicle applications of natural gas. CNG combustion yields significant reductions in particulate emissions compared to diesel. However, the inherently low flame speed of CNG decreases thermal efficiency and increases toxic aldehyde emissions in ICEs, requiring optimization of spark timing. Due to its increased flame speed compared to methane and liquid fuels, hydrogen has been shown to “assist” natural gas combustion in that it decreases combustion duration, reduces minimum spark advance for best torque (MBT timing), enhances combustion efficiency and can reduce emissions of unburned fuel. The literature contains many studies that demonstrate hydrogen’s ability to burn faster than other fuels and that acknowledge hydrogen’s uniqueness compared to other fuels in terms of its mass diffusivity, wide flammability range, and minimum ignition energy, but these studies rarely attempt to explain such characteristics in a scientific manner. Most review articles focus on a particular aspect of technical implementation of hydrogen as a combustible fuel in lieu of a holistic view of hydrogen assisted combustion of hydrocarbon fuels in ICEs. The intention of the present work was to build on the understanding of the role of hydrogen in the spark-ignited combustion of natural gas, by confirming common findings in the literature, namely that the addition of hydrogen to natural gas enables spark retard due to enhanced early flame development, and that retarded spark at MBT for HCNG results in concentrated heat release near TDC, improving the efficiency compared to CNG alone. The primary objective of the present work is to perform detailed heat release analysis to evaluate the following hypothesis: while swirl can be employed to improve the sluggish early flame development of CNG, using hydrogen to supplant swirl enables improved early flame development without compromising engine efficiency due to convective heat losses caused by enhanced fluid motion. The present work employs a single-cylinder spark-ignited engine to study the effects of intake-induced turbulence and turbulence intensity on hydrogen assisted natural gas (HCNG) combustion. The effects with hydrogen assisted combustion are examined through comparison with combustion of CNG alone. Experiments were conducted at 2000 rpm with both fixed spark timing and adjusting spark to maintain MBT, as well as at 2750 rpm with MBT timing alone. Each study was conducted at 1.5 bar brake mean effective pressure (BMEP), stoichiometric equivalence ratio and MBT timing for each fuel; fueling rate was fixed as the throttle was opened to achieve leaner conditions (engine load is not fixed). Results with a high level of in-cylinder swirl (one intake port fully blocked) were compared to results with a quiescent in-cylinder flow (fully opened intake ports).