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Argonne study identifying fuel consumption penalties for CNG use in conventional light-duty vehicles; optimization pathways
18 May 2012
|Light-duty vehicle fuel economy penalties for CNG in conventional engines, with and without scaling for performance equivalence. Source: ANL. Click to enlarge.|
Preliminary findings from a study by researchers at Argonne National Laboratory (ANL) show that current compressed natural gas (CNG) technology applied in conventional light-duty vehicles leads to a 2% fuel consumption penalty when the engine is not resized (i.e., the CNG-fueled engine has lower performance) and up to a 12% fuel consumption penalty when the engine is resized (i.e., “up-sizing”) to deliver comparable performance to the gasoline-fueled version.
Using OEM engine maps for gasoline and CNG for the same engine, ANL found that use of CNG fuel in the same engine resulted in lower performance: 112 kW of output for CNG vs. 136 kW for gasoline, with 0-60 mph performance of 10.2 seconds for CNG vs. 9.5 seconds for gasoline.
When scaling the CNG engine up for comparable performance (9.5 seconds 0-60 mph), resulting in 145 kW of output, fuel economy dropped to 32.1 mpgge for CNG, versus the 36.6 mpg for the gasoline baseline.
Two percent, you can live with. When you start to go to 12%, we have to understand where that comes from and how you can mitigate it.—Aymeric Rousseau
Most of the fuel consumption penalties occur at low load on the UDDS drive cycle, said ANL’s Dr. Aymeric Rousseau in his presentation of results at the 2012 DOE Hydrogen Program and Vehicle Technologies Annual Merit Review. On the UDDS cycle, the fuel consumption penalty was 3.3% without scaling the engine and 14% with scaling compared to the highway (HWEFT) results of 0% and 9.1%.
Hybridization would lower the CNG penalty, he noted. An ongoing phase of the project is the evaluation of the fuel displacement potential on several electric drive vehicles (HEVs, PHEVs) for light duty applications.
The overall objective of the project is to evaluate the fuel displacement potential of CNG, LNG and LPG vehicles—light-, medium-, and heavy-duty. The project seeks to identify what vehicle applications and powertrain configurations would best benefit from these fuels and how vehicle control strategies should be changed to optimize the fuel displacement.
Accordingly, the project plan for this year includes implementing medium- and heavy-duty (MD&HD) engine data, as well as including LNG and LPG assessments along with CNG. This will entail defining component sizing for each MD&HD application, selecting the drive cycles for each MD&HD application, and evaluating the fuel displacement potential on several electric drive vehicles (HEVs, PHEVs) for medium- and heavy-duty applications.
Potential work for the future would be to evaluate the potential of future CNG, LNG, LPG engine technologies such as direct injection, as well as to look at other sources for optimization such as gearing.
VSS078: Fuel Displacement & Cost Potential of CNG, LNG, and LPG Vehicles (2012 DOE Hydrogen Program and Vehicle Technologies Annual Merit Review) Presentations will be posted in several weeks at www.vehicles.energy.gov.
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