Engine Exhaust Heat Recovery

Topics: Energy, Thermodynamics, Internal combustion engine Pages: 6 (1724 words) Published: December 1, 2011

KAVIRAJ.P* DINAKARAN.K* *Pre-final year Automobile students, Madras Institute of Technology, Anna University, Chennai

Kavi.royalz@gmail.com demon.deen@gmail.com

Today hybrid concepts with energy storage are ways to correct the poor piston engine efficiency at reduced power. There are at least 2 other ways to improve the piston engine efficiencies: exhaust heat recovery and detonation combustion mode. Exhaust heat recovery could further be used on today hybrid engines to further increase its overall efficiency. The energy components carried away by the exhaust, are primarily results of incomplete combustion, incomplete expansion, sensible heat, and latent heat of the water vapor created by burning of the hydrogen component of fuel. This paper provides a simple analysis of a typical vehicle energy and power demand in acceleration and steady driving, and looks at the management of heat recovery energy and power, which could reach the 25% range in steady driving and much more in city driving (available energy increasing with decreased engine efficiency). Quasiturbine systems using rankine cycle and Brayton cycle using are described as the best possible heat recovery techniques, which also could apply to geothermal, industrial processes, solar, biomass combustion and to nuclear heat as well. The extremely compact and efficient Quasiturbine technology is needed to accomplish these goals.

Key terms:
Quasiturbine, piston engine efficiencies, Rankine cycle, Brayton cycle, exhaust heat recovery, detonation combustion mode

The Toyota Prius and others have proved that the hybrid electric concept can greatly improve fuel mileage. Unfortunately, all hybrids do not provide equivalent efficiency. A different type of hybrid which recovers part of the wasted heat energy from the engine can improve the efficiency over the basic engine efficiency without requiring energy storage.

A typical internal combustion engine (ICE) uses only a small part of the energy available from the burned fuel to propel the vehicle. The excess energy is wasted and goes out into the atmosphere through the exhaust gasses and the air of the cooling system. Some of this wasted heat energy can be recovered and converted into useful mechanical energy to help propel the vehicle. The purpose of this paper is to investigate methods for recovering some of exhaust gas heat energy, which is rejected by the typical ICE used in most automobiles, and converting the recovered energy into mechanical energy to help drive the load.

The power demand requirements for most modern automobiles vary greatly over the various driving conditions encountered. Detailed calculations will be provided which illustrate how the power requirements were derived. The data are derived for a full sized sedan, such as the 2006 Ford 500, weighs 4000 pounds (lbs) with the driver, and has a 200 HP engine. At highway speeds of 70 MPH, only about 33 HP are required to overcome air drag and tire rolling friction. At 55 MPH only about 18 HP are required. In much of city driving, the driving speed will be 40 MPH or less where the power requirement for overcoming air drag and rolling friction is only about 10 HP. The 200 HP engine is needed to provide power for climbing hills, accelerating, and overall performance desired by the drivers. Thus, the power requirement varies over a ratio of greater than 200 / 10 = 20. A heavier car would require even more peak power to provide the performance demanded by most of the drivers, but very little extra power would be needed to overcome air drag and rolling friction.

The energy from the fuel supplied...
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