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Fuel Combustion

Energy Recovery in Passenger Cars

[+] Author and Article Information
Alberto A. Boretti

Department of Mechanical and Aerospace Engineering,  Missouri University of Science and Technology, Rolla, MO 65409

J. Energy Resour. Technol 134(2), 022203 (Mar 19, 2012) (8 pages) doi:10.1115/1.4005699 History: Received August 25, 2011; Revised December 21, 2011; Published March 16, 2012; Online March 19, 2012

The turbocharged direct injection stoichiometric spark ignition gasoline engine has less than diesel full load brake engine thermal efficiencies and much larger than diesel penalties in brake engine thermal efficiencies reducing the load. This engine has, however, a much better power density, and therefore may operate at much higher brake mean effective pressure (BMEP) values over driving cycles thus reducing the fuel economy penalty of the vehicle. This engine also has the advantage of the very well developed three way catalytic (TWC) converter after treatment to meet future emission regulations. Replacement of fossil gasoline with renewable gasoline-like fuels has major advantages. Ethanol and methanol have larger than gasoline resistance to knock and heat of vaporization, and this ultimately translates in larger than gasoline compression ratio and boost pressure and spark advances closer to maximum brake torque producing better efficiencies both full and part load. For the specific of these novel turbocharged direct injection stoichiometric spark ignition renewable gasoline-like engines coupled to a hybrid-electric power train, the paper considers the option to boost the total fuel conversion efficiency generating both mechanical and electric energy. When the internal combustion engine operates, significant fuel energy is lost in both the exhaust and the coolant. Part of this energy is recovered here by using organic Rankine cycle (ORC) systems fitted to both the exhaust and the coolant, with their expanders driving generators charging the battery of the car. The exhaust and the coolant organic Rankine cycle are effective in increasing the amount of fuel energy converted in usable power over the full range of loads and speeds. The organic Rankine cycle system fitted on the exhaust permits to increase the usable power versus the fuel energy flow rate of a 3.4% on average, with top improvements up to 6.4%. The system is effective particularly at high speeds and loads. The organic Rankine cycle system fitted on the coolant permits to increase the usable power versus the fuel energy flow rate of a 1.7% on average, with top improvements up to 2.8%. The system is effective particularly at low speeds and loads. The two combined organic Rankine cycle systems permit to increase the usable power versus the fuel energy flow rate of a 5.1% on average, with top improvements up to 8.2%.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Brake efficiency of the gasoline engine

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Figure 2

Brake efficiency of the ethanol engine

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Figure 3

Brake efficiency of the methanol engine

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Figure 4

Simplified schematic diagram of the heat recovery system (exhaust)

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Figure 5

Percentage of fuel energy recovered with a coolant ORC fitted to the gasoline engine

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Figure 6

Percentage of fuel energy recovered with three exhaust ORCs fitted to the gasoline engine

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Figure 7

Percentage of fuel energy recovered with both coolant and exhaust ORCs fitted to the gasoline engine

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Figure 8

Augmented efficiency (brake power + expander − pump power ORCs engine coolant and exhaust)/fuel energy flow rate of the gasoline engine with fitted the coolant and exhaust ORCs

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Figure 9

Augmented efficiency (brake power + expander − pump power ORCs engine coolant and exhaust)/fuel energy flow rate of the ethanol engine with fitted the coolant and exhaust ORCs

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Figure 10

Augmented efficiency (brake power + expander − pump power ORCs engine coolant and exhaust)/fuel energy flow rate of the methanol engine with fitted the coolant and exhaust ORCs

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