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RESEARCH PAPERS

Improving Ethanol Life Cycle Energy Efficiency by Direct Utilization of Wet Ethanol in HCCI Engines

[+] Author and Article Information
Joel Martinez-Frias, Salvador M. Aceves, Daniel L. Flowers

 Lawrence Livermore National Laboratory, 7000 East Avenue, Mail Stop L-644, Livermore, CA 94551saceves@llnl.gov

J. Energy Resour. Technol 129(4), 332-337 (Jun 29, 2007) (6 pages) doi:10.1115/1.2794768 History: Received November 14, 2005; Revised June 29, 2007

Homogeneous charge compression ignition (HCCI) is a new engine technology with fundamental differences over conventional engines. HCCI engines are intrinsically fuel flexible and can run on low-grade fuels as long as the fuel can be heated to the point of ignition. In particular, HCCI engines can run on “wet ethanol:” ethanol-in-water mixtures with high concentration of water. Considering that much of the energy required for processing fermented ethanol is spent in distillation and dehydration, direct use of wet ethanol in HCCI engines considerably shifts the energy balance in favor of ethanol. The results of the paper show that a HCCI engine with efficient heat recovery can operate on a mixture of 35% ethanol and 65% water by volume while achieving a high brake thermal efficiency (38.7%) and very low NOx (1.6ppm, clean enough to meet any existing or oncoming emissions standards). Direct utilization of ethanol at a 35% volume fraction reduces water separation cost to only 3% of the energy of ethanol and coproducts (versus 37% for producing pure ethanol) and improves the net energy gain from 21% to 55% of the energy of ethanol and coproducts. Wet ethanol utilization is a promising concept that merits more detailed analysis and experimental evaluation.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Net energy balance for ethanol (2-3). The full circle represents the energy output of ethanol and coproducts. The figure shows wedges indicating energy consumption in all stages of ethanol production from corn, as a percent of the heating value of ethanol and coproducts. The energy that remains after accounting for all the energy consumption is the net energy gain, which has two components: net energy in the ethanol and net energy in the coproducts.

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Figure 2

Energy required for ethanol distillation, as a fraction of the lower heating value of ethanol, as a function of the ethanol-in-water concentration by volume after distillation. It is assumed that the concentration of ethanol at the beginning of the distillation process is 12% by volume.

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Figure 3

Schematic of the HCCI engine system operating on wet ethanol. The numbers in the figure show pressures and temperatures for operation with a 35% ethanol in water by volume mixture as the supplied fuel. The 420K temperature inside the engine refers to the charge temperature at the beginning of the compression stroke.

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Figure 4

Lower heating value divided by the latent heat of vaporization for mixtures of ethanol and water as a function of the ethanol volume concentration. The dotted horizontal line indicates the point at which the ethanol heating value is just enough to vaporize the mixture, corresponding to 11% ethanol in water by volume.

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Figure 5

Net energy balance for ethanol, considering production of a 35% ethanol in water by volume mixture appropriate as fuel for a HCCI engine. The figure shows wedges indicating energy consumption in all stages of ethanol production from corn, as a percent of the heating value of ethanol and coproducts. The energy that remains after accounting for all the energy consumption is the net energy gain, which has two components: net energy in the ethanol and net energy in the coproducts.

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