SGS Automotive has recently completed a study for the Coordinating Research Council to investigate the effect of fuel composition on the performance and emissions of light-duty Natural Gas Vehicles (NGVs). 

The demand for NGVs has increased as domestically-produced natural gas has grown dramatically in the U.S. with the implementation of new gas extraction technologies. Compressed Natural Gas (CNG) has become a cost effective and clean burning alternative to gasoline and diesel fuel.  However, CNG fuel properties vary widely across the country.  The objective of this study was to test a wide range of CNG fuel compositions in three modern NGVs to determine the effect on the performance and emissions.  Test vehicles included the 2012 Honda Civic GX, 2014 Volkwagen Golf TGI, and 2014 Dodge Ram 2500 CNG. 

Seven CNG test fuels were prepared for the study.   The primary fuel properties of interest were Methane Number, Wobbe Index, non-methane hydrocarbon content, and inert gas content. Vehicle testing was performed at the SGS Automotive emissions laboratory located in Aurora, Colorado.   Engine-out and tailpipe emissions were measured to isolate the cause of emissions changes.  An in-cylinder combustion analysis system was used to perform knock investigations.

Total hydrocarbon and methane emissions increased with lower Wobbe Index fuels for all three vehicles tested.  One vehicle was significantly more sensitive to fuel quality and produced significantly higher NOx emissions when run on the lower Wobbe Index fuels.   Engine knock was not observed under high load and high temperature operation, indicating that the combination of compression ratio, EGR, ignition timing, and valve timing employed on these vehicles was able to accommodate the lowest Methane Number fuel under the conditions tested.

The final report for the Coordinating Research Council E-109 study may be downloaded for free from the CRC website, at:

http://www.crcao.org/reports/recentstudies2015/E-109/CRC_E-109_Final_Report_May2015.pdf