# Cost, Effectiveness, and Deployment of Fuel Economy Technologies for Light-Duty Vehicles(2015)

## Chapter: Appendix E: SI Engine Definitions and Efficiency Fundamentals

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Page 380
Suggested Citation:"Appendix E: SI Engine Definitions and Efficiency Fundamentals." National Research Council. 2015. Cost, Effectiveness, and Deployment of Fuel Economy Technologies for Light-Duty Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/21744.
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Appendix E

SI Engine Definitions and Efficiency Fundamentals

The following definitions are helpful in discussing SI engine efficiency fundamentals (Heywood 1988):

Mean Effective Pressure (MEP) = Work per cycle/displaced volume

Indicated Mean Effective Pressure (IMEP) = Work delivered to the piston over the compression and expansion strokes, per cycle per unit displaced volume

Friction Mean Effective Pressure (FMEP) = Total friction work per cycle per unit displaced volume

BMEP can be calculated as follows:

 Brake Mean Effective Pressure (BMEP) = IMEP – FMEP (1)

FMEP consists of the following three components:

Pumping Mean Effective Pressure (PMEP) = Work per cycle done by the piston on the in-cylinder gases during the inlet and exhaust strokes. PMEP is positive for naturally aspirated engines and negative for supercharged and turbocharged engines at high loads.

Rubbing Friction Mean Effective Pressure (RFMEP) = Work per cycle dissipated per cycle in overcoming friction due to relative motion of adjacent components in the engine.

Accessory Mean Effective Pressure (AMEP) = Work per cycle required to drive engine accessories (pumps, fans, alternator, etc.) essential to engine operation.

Therefore, FMEP can be expressed as follows:

 FMEP = PMEP + RFMEP + AMEP (2)

Brake thermal efficiency (BTE) is subsequently defined as the ratio of work delivered divided by the heating value of the fuel (generally lower heating value since the water in the exhaust is in vapor form):

 BTE = BMEP × displaced volume / (mf × QLHV) (3)

Where: mf = mass flow rate of fuel

QLHV = Lower heating value of fuel

A similar expression is used to calculate indicated thermal efficiency (ITE).

The relationships discussed above are shown in Wade et al. (1984) for an engine operating condition representative of the FTP drive cycle.

REFERENCES

Heywood, J.B. 1988. Internal Combustion Engine Fundamentals. New York: McGraw-Hill.

Wade, W.R., J. E. White, C. M. Jones, C. E. Hunter, and S. P. Hansen. 1984. Combustion, Friction and Fuel Tolerance Improvements for the IDI Diesel Engine. SAE Technical Paper 840515.

Page 380
Suggested Citation:"Appendix E: SI Engine Definitions and Efficiency Fundamentals." National Research Council. 2015. Cost, Effectiveness, and Deployment of Fuel Economy Technologies for Light-Duty Vehicles. Washington, DC: The National Academies Press. doi: 10.17226/21744.
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Next: Appendix F: Examples of Friction Reduction Opportunities for Main Engine Components »
Cost, Effectiveness, and Deployment of Fuel Economy Technologies for Light-Duty Vehicles Get This Book
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The light-duty vehicle fleet is expected to undergo substantial technological changes over the next several decades. New powertrain designs, alternative fuels, advanced materials and significant changes to the vehicle body are being driven by increasingly stringent fuel economy and greenhouse gas emission standards. By the end of the next decade, cars and light-duty trucks will be more fuel efficient, weigh less, emit less air pollutants, have more safety features, and will be more expensive to purchase relative to current vehicles. Though the gasoline-powered spark ignition engine will continue to be the dominant powertrain configuration even through 2030, such vehicles will be equipped with advanced technologies, materials, electronics and controls, and aerodynamics. And by 2030, the deployment of alternative methods to propel and fuel vehicles and alternative modes of transportation, including autonomous vehicles, will be well underway. What are these new technologies - how will they work, and will some technologies be more effective than others?

Written to inform The United States Department of Transportation's National Highway Traffic Safety Administration (NHTSA) and Environmental Protection Agency (EPA) Corporate Average Fuel Economy (CAFE) and greenhouse gas (GHG) emission standards, this new report from the National Research Council is a technical evaluation of costs, benefits, and implementation issues of fuel reduction technologies for next-generation light-duty vehicles. Cost, Effectiveness, and Deployment of Fuel Economy Technologies for Light-Duty Vehicles estimates the cost, potential efficiency improvements, and barriers to commercial deployment of technologies that might be employed from 2020 to 2030. This report describes these promising technologies and makes recommendations for their inclusion on the list of technologies applicable for the 2017-2025 CAFE standards.

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