EHPG TRANSFORMS HEAT TO POWER AND ELECTRICITY FOR TRUCKS, HYBRIDS
Automotive drivetrains use fuel to power vehicles which produces a tremendous amount of heat, one-third of which is lost through the exhaust system.
That wasted heat can be a valuable resource, however. For a number of years, Faurecia has produced exhaust heat recovery systems that capture exhaust heat and use it to warm vehicle interiors, allowing hybrid cars to switch to their electric mode sooner. Now, Faurecia has developed the Exhaust Heat Power Generation (EHPG), a system to convert exhaust heat to electricity and power.
Exhaust Heat Power Generation (EHPG)
EHPG produces power that can be used to directly drive trucks or to extend the use of electrical power in hybrid vehicles. EHPG harnesses the principles of the Rankine cycle to convert heat from exhaust gases to electrical power.
In much the way electricity is generated in power plants, EHPG employs a heat exchanger (evaporator) located in the exhaust flow. The thermal energy in the pipe is transferred to a so-called working fluid. The resulting pressurized steam powers an expander, which could be a turbine. The expander’s shaft can be attached to a truck’s gearbox to turn the wheels directly. In hybrid passenger cars, the expander is coupled to a generator that creates electricity, which is stored in the vehicle’s battery. After steam leaves the expander, it moves through a condenser where it is converted to liquid again, transferring its residual heat to the vehicle’s cooling system. Finally, a pump pushes the liquid back to the evaporator, creating a closed-loop system.
In both applications — direct power for trucks and electrical power for hybrids — the vehicles consume less fuel, and therefore hydrocarbon emissions are reduced. In trucks, overall fuel economy improves by 5 percent or more, even taking into account EHPG’s additional weight, and the system can produce 10 to 15 kilowatts of mechanical power, reducing the power and fuel demands on the vehicle’s engine. Using EHPG would mean saving around 20,000 liters of diesel fuel — or 40 full tanks — and avoid 50 metric tons of CO2 over a truck’s lifetime. EHPG is estimated to pay back its cost in just two years in the form of fuel savings.
In passenger vehicles, a smaller EHPG system adds just 10 to 15 kilograms of weight but generates 1 to 2 kilowatts of additional electrical power, adding to the electricity stored in the battery and thereby delaying the need to switch to the gasoline drivetrain. In hybrids EHPG nets a fuel economy improvement of about 7 percent. Moreover, EHPG is expected to reduce CO2 emissions by 9 g per km, which would sum up to 2.5 metric tons less CO2 over a hybrid vehicle’s lifetime.
PRODUCING ELECTRICAL POWER WITH NO MOVING PARTS
Faurecia also is investigating another method of converting waste heat to electricity. The thermo-electric generator, or TEG, uses the Seebeck effect to transform heat to electricity with no moving parts.
The TEG consists of an array of semi-conductors on a substrate that produce an electrical current when a temperature differential is applied to them. Cold water from the vehicle’s cooling system lowers the temperature on one side of the array while exhaust gases heat the other side. This heat gradient causes the semiconductors to release electrons that flow from the hot side to the cold side until an equilibrium is attained. By maintaining the difference in temperatures between the heat source and heat sink, the current flow is sustained.
The TEG can be used on all types of passenger cars — hybrid, all-electric and standard vehicles – to furnish additional electrical power. It is even more compact than EHPG; it can yield a fuel savings of 3 to 4 percent at its peak; and it enables vehicle designers to incorporate a smaller alternator — or even none — to recharge the battery, thereby saving on weight.
The TEG is expected to first be available after 2022, once its efficiency and cost factors are optimized.
A LIGHTER EXHAUST PIPE
Faurecia’s focus on lightweighting to improve fuel economy incorporates virtually every system inside, outside and under the car – even the exhaust pipe. Faurecia’s new Resonance Free Pipe™ (RFP™) contributes to this goal by eliminating the need for small silencers, known as resonators.
Resonators inside tailpipes break long sound waves to reduce unwanted frequencies. RFP™ eliminates these long waves without resonators by venting acoustic pressure at the optimum point in the exhaust system through a micro-perforated material. While most of the exhaust gas continues to exit the system through the tailpipe, this very minute venting of treated exhaust gas allows for a simpler system design that provides 4 to 11 pounds of weight savings in a more compact package. RFP™ can potentially be used in any light-duty vehicle.