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ARTICLE IN PRESS
Energy xxx (2010) 1–7
Contents lists available at ScienceDirect
Energy journal homepage: www.elsevier.com/locate/energy
A highly efficient six-stroke internal combustion engine cycle with water injection for in-cylinder exhaust heat recovery
James C. Conklin, James P. Szybist*
Oak Ridge National Laboratory, 2360 Cherahala Blvd, Knoxville, TN 37932, USA
a r t i c l e i n f o
Article history: Received 9 September 2009 Received in revised form 3 December 2009 Accepted 8 December 2009 Available online xxx Keywords: Engine efficiency Six-stroke cycle Water injection Steam cycle
a b s t r a c t
A concept adding two strokes to the Otto or Diesel engine cycle to increase fuel efficiency is presented here. It can be thought of as a four-stroke Otto or Diesel cycle followed by a two-stroke heat recovery steam cycle. A partial exhaust event coupled with water injection adds an additional power stroke. Waste heat from two sources is effectively converted into usable work: engine coolant and exhaust gas. An ideal thermodynamics model of the exhaust gas compression, water injection and expansion was used to investigate this modification. By changing the exhaust valve closing timing during the exhaust stroke, the optimum amount of exhaust can be recompressed, maximizing the net mean effective pressure of the steam expansion stroke (MEPsteam). The valve closing timing for maximum MEPsteam is limited by either 1 bar or the dew point temperature of the expansion gas/moisture mixture when the exhaust valve opens. The range of MEPsteam calculated for the geometry of a conventional gasoline engine and is from 0.75 to 2.5 bars. Typical combustion mean effective pressures (MEPcombustion) of naturally aspirated gasoline engines are up to 10 bar, thus this concept has the potential to significantly increase the engine efficiency and fuel economy. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction In internal combustion engines, a significant amount
Energy xxx (2010) 1–7
Contents lists available at ScienceDirect
Energy journal homepage: www.elsevier.com/locate/energy
A highly efficient six-stroke internal combustion engine cycle with water injection for in-cylinder exhaust heat recovery
James C. Conklin, James P. Szybist*
Oak Ridge National Laboratory, 2360 Cherahala Blvd, Knoxville, TN 37932, USA
a r t i c l e i n f o
Article history: Received 9 September 2009 Received in revised form 3 December 2009 Accepted 8 December 2009 Available online xxx Keywords: Engine efficiency Six-stroke cycle Water injection Steam cycle
a b s t r a c t
A concept adding two strokes to the Otto or Diesel engine cycle to increase fuel efficiency is presented here. It can be thought of as a four-stroke Otto or Diesel cycle followed by a two-stroke heat recovery steam cycle. A partial exhaust event coupled with water injection adds an additional power stroke. Waste heat from two sources is effectively converted into usable work: engine coolant and exhaust gas. An ideal thermodynamics model of the exhaust gas compression, water injection and expansion was used to investigate this modification. By changing the exhaust valve closing timing during the exhaust stroke, the optimum amount of exhaust can be recompressed, maximizing the net mean effective pressure of the steam expansion stroke (MEPsteam). The valve closing timing for maximum MEPsteam is limited by either 1 bar or the dew point temperature of the expansion gas/moisture mixture when the exhaust valve opens. The range of MEPsteam calculated for the geometry of a conventional gasoline engine and is from 0.75 to 2.5 bars. Typical combustion mean effective pressures (MEPcombustion) of naturally aspirated gasoline engines are up to 10 bar, thus this concept has the potential to significantly increase the engine efficiency and fuel economy. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction In internal combustion engines, a significant amount
References: [1] Rodriguez L. Calculation of available-energy quantities. Thermodynamics – second law analysis. American Chemical Society Symposium Series 1980; 122:39–59. [2] Dyer LH. Internal combustion engine. United States patent 1,339,176; 1920. [3] Rohrbach H, Tamins R. Engine having alternate internal-combustion and fluid pressure power strokes. United States patent 2,671,311; 1954. [4] Tibbs RC. Six cycle combustion and fluid vaporization engine. United States patent 3,964,263; 1976. [5] Kellogg-Smith O. Internal combustion and steam engine. United States patent 4.143,518; 1979. [6] Larsen GJ. Engine with a six-stroke cycle, variable compression ratio, and constant stroke. United States patent 4,736,715; 1988. [7] Prater DM. Multiple stroke engine having fuel and vapor charges. United States patent 6,253,745; 2001. [8] Crower B. Method and apparatus for operating an internal combustion engine. United States patent application 20070022977; 2005. [9] Çengel YA, Boles MA. Thermodynamics: an engineering approach. 5th ed. Boston: McGraw-Hill; 2005. [10] Delft University of Technology, Energy Technology Section. FluidProp: software for the calculation of thermophysical properties of fluids. The Netherlands. See also, http://www.FluidProp.com; 2004. [11] Heywood JB. Internal combustion engine fundamentals. New York: McGrawHill; 1998. Please cite this article in press as: Conklin JC, Szybist JP, A highly efficient six-stroke internal combustion engine cycle with water injection for..., Energy (2010), doi:10.1016/j.energy.2009.12.012