September 6, 2014

The goal of this project is to assess compressed natural gas (CNG) fueled vehicles and evaluate their suitability as alternatives to traditional gasoline powered passenger vehicles. First, the combustion process, specific fuel consumption, and overall efficiency of a CNG four-stroke engine will be discussed and compared to a typical gasoline four-stroke engine. Environmental benefits, will then be discussed, including reduced vehicle emissions and lower production greenhouse gas emissions. Finally, practical concerns of using CNG as a fuel source, such as access to fueling stations and dangers of vehicular accidents, will be presented.
There are approximately 1 billion passenger vehicles in the world and about 25% of those are in the United States. The vast majority of these vehicles are spark ignition, gasoline fueled vehicles. Recently, environmental and political pressures have highlighted the need for alternative fuels that are more readily available and the combustion of which causes less environmental pollution. Compressed natural gas (95% methane) has emerged as a possible fuel due to its relative abundance and cleaner burning properties.
The viability of using CNG for personal vehicles will be explored. This will include a theoretical efficiency study, a comparison of vehicle emissions with conventional automobiles, and a discussion of pragmatic realities of operating an alternative energy vehicle.
The combustion process, specific fuel consumption, and overall efficiency of a CNG four-stroke engine will be discussed. CNG has a lower energy content per unit volume than gasoline, but CNG fueled engines can operate at higher compression ratios and therefore higher efficiencies. The tradeoffs involved will be contrasted.
The stoichiometric equations for combustion indicate the resulting exhaust gases that will make up the vehicle emissions. The predicted emissions will be compared to test data.
Additional lifecycle greenhouse gas emission differences will be discussed.
The practical concerns to be investigated include refueling, fuel concerns during accidents, higher initial cost, and less range due to storage tank size.
-Microsoft Office Software (Microsoft Word, Excel, Power Point)
-Combustion textbooks
-Literature discussing gasoline and CNG vehicle emissions
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The end result of this project will be to determine if CNG powered vehicles are theoretically more efficient, better for the environment, and whether they are acceptable for everyday use.
Table 1 – Proposed Project Milestones
Task Date
Complete Project Proposal
Complete Background / Previous Work
Complete Theory
Complete Hand Calculations of
Combustion Efficiency
Research Emissions and Environmental
Impact Finished
Review Real-World Issues
Insert Figures
Complete All Analysis
September 9
September 14
September 30
September 30
October 14
October 27
October 27
October 27
Complete Results
Complete Initial Report Draft
Complete Report
Table 2 - Deadlines
November 3
November 3
November 17
Task
Tentative Project Proposal Draft
Project Proposal Draft
First Progress Report
Second Progress Report
Final Draft Report
Preliminary Final Report
Final Report
ECD
-
September 8
September 15
October 13
November 3
November 17
December 8
Date
September 5
September 12
September 26
October 17
November 7
November 28
December 12
As the pressure to find an abundant, clean burning fuel has increased, significant research into natural gas has been performed. It is known that the thermal efficiency of an engine increases with the compression ratio. Zheng in Reference [6], experimentally determined that increasing the compression ratio from ~9:1 for gasoline powered engines to ~12:1 allowed for increased efficiency without significantly increasing unwanted emissions. In addition to higher compression ratios, Reference [1] discusses how operating natural gas engines at an air/fuel ratio leaner than stoichiometric can result in acceptable power with
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lower emissions. However, lean operation and high compression ratios can result in high combustion temperatures. That leads to the formation of large amounts of NO x
as discussed in Reference [3]. Reference [5] discusses one approach to keep the NO x production at low levels: the addition of supplementary hydrogen as a secondary fuel.
[1] Haeng Muk Cho, Bang-Quan He. Spark ignition natural gas engines – A review . Energy
Conversion and Management 48, 2007.
[2] Heywood, John B. Internal Combustion Engine Fundamentals . McGraw Hill, 1988.
Print.
[3] Korakianitis, T., Namasivayam, A. M., Crookes, R. J. Natural-gas fueled spark-ignition
(SI) and compression ignition (CI) engine performance and emissions.
Progress in
Energy and Combustion Science 37, 2011.
[4] Norton, Robert L. Design of Machinery – An Introduction to the Synthesis and Analysis of Mechanisms and Machines. 3rd ed. McGraw Hill, 2004. Print.
[5] Tunestal, P., Christensen, M., Einewall, P., Andersson, T., and Johansson, B. Hydrogen
Addition For Improved Lean Burn Capability of Slow and Fast Burning Natural Gas
Combustion Chambers.
Society of Automotive Engineers 2002-01-2686, 2002.
[6] Zheng, J. J., Wang, J. H., Wang, B., and Huang, Z. H. Effect of the compression ratio on the performance and combustion of a natural-gas direct-injection engine.
IMechE: Vol.
223 Part D: J. Automobile Engineering, 2009.
1) Progress in Energy and Combustion Science
2) International Journal of Vehicle Design
3) Energy
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