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Automotive thermoelectric generator
An automotive thermoelectric generator (ATEG) is a device that utilizes the Seebeck effect in order to recover lost heat from an internal combustion engine powered vehicle, and generate electricity with it. A typical ATEG consists of four main elements: A hot-side heat exchanger, a cold-side heat exchanger, thermoelectric materials, and compression assembly system. ATEGs can be classified according to their hot-side heat exchanger to exhaust-based ATEGs and coolant-based ATEGs. The first type converts the heat lost in the IC engine exhaust, while the second type converts the heat lost in the engine coolant, into electricity.
This paper proposes and implements a thermoelectric waste heat energy recovery system for internal combustion engine automobiles, including gasoline vehicles and hybrid electric vehicles. The key is to directly convert the heat energy from automotive waste heat to electrical energy using a thermoelectric generator, which is then regulated by a DC–DC converter to charge a battery using maximum power point tracking. Hence, the electrical power stored in the battery can be maximized. Both analysis and experimental results demonstrate that the proposed system can work well under different working conditions, and is promising for automotive industry.
INTRODUCTION
Even a highly efficient combustion engine converts only about one-third of the energy in the fuel into mechanical power serving to actually drive the vehicle. The rest is lost through heat discharged into the surroundings or, quite simply, leaves the vehicle as “waste heat”. Clearly, this offers a great potential for the further reduction of CO2 emissions which the engineers are seeking to use through new concepts and solutions.
The generation of electric power in the motor vehicle is a process chain subject to significant losses. Quite simply because the chemical energy contained in the fuel is first converted into mechanical energy and then, via generator, into electric power. Now the engineers are working on a technology able to convert the thermal energy contained in the exhaust gas directly into electric power. This thermoelectric process of recovering energy and generating power by means of semi-conductor elements has already been used for decades by NASA, the US Space Agency, in space probes flying into outer space.
Until just a few years ago, however, such thermoelectric generators (TEGs) were unsuitable for use in the automobile due to their low level of efficiency. But since significant progress has been made in materials research in recent times, the performance and output of such modules has increased significantly. To generate electric power in the vehicle a thermoelectric generator is integrated in the exhaust manifold.
While the electric power such a system is able to generate is still relatively small at a maximum of 200 W, rapid progress in materials research already makes the ambitious objective of generating up to 1,000 W a realistic and by all means feasible proposition. This energy regeneration system also offers additional effects, such as providing the engine or the heating system with extradriven heat when starting the engine cold. TEG offers its benefits when motoring is really fun, that is when accelerating and enjoying the power of the vehicle.
Now coming to the point of increasing volumetric efficiency in an engine using TEG ,here we are using a turbine and a pump arrangement(similar to a turbocharger) which is driven by the electrical energy generated by the TEG, which uses the engine heat.
Operation principles
In ATEGs, thermoelectric materials are packed between the hot-side and the cold-side heat exchangers. The temperature difference between the two surfaces of the thermoelectric module(s) generates electricity. The compression assembly system aims to decrease the thermal contact resistance between the thermoelectric module and the heat exchanger surfaces. In coolant-based ATEGs, the cold side heat exchanger uses engine coolant as the cooling fluid, while in exhaust-based ATEGs, the cold-side heat exchanger uses ambient air as the cooling.
The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice versa. A thermoelectric device creates a voltage when there is a different temperature on each side. Conversely when a voltage is applied to it, it creates a temperature difference (known as the Peltier effect). At atomic scale (specifically, charge carriers), an applied temperature gradient causes charged carriers in the material, whether they are electrons or electron holes, to diffuse from the hot side to the cold side, similar to a classical gas that expands when heated; hence, the thermally induced current.
Volumetric efficiency
Volumetric efficiency in internal combustion engine design refers to the efficiency with which the engine can move the charge into and out of the cylinders. More specifically, volumetric efficiency is a ratio (or percentage) of what quantity of fuel and air actually enters the cylinder during induction to the actual capacity of the cylinder under static conditions. Therefore, those engines that can create higher induction manifold pressures - above ambient - will have efficiencies greater than 100%. Volumetric efficiencies can be improved in a number of ways, but most notably the size of the valve openings compared to the volume of the cylinder and streamlining the ports. Engines with higher volumetric efficiency will generally be able to run at higher speeds (commonly measured in RPM) and produce more overall power due to less parasitic power loss moving air in and out of the engine.
WORKING
To increase the volumetric efficiency of an engine more charge(air) has to be driven or sent into the combustion chamber. To produce this effect we are using the turbine and pump arrangement(similar to a turbocharger) which is driven by a motor coupled to it, the motor gets the power to drive the turbine and pump arrangement by power generated from the TEG.
When the turbine is driven the pump starts creating suction(low pressure) which is less than the atmospheric pressure 1 atm (approximately 14.7 psi, or 1 bar), as a result there ultimately will be a limit to the pressure difference across the intake valves and thus the amount of airflow entering the combustion chamber. Since the above process increases the pressure at the point where air is entering the cylinder, a greater mass of air (oxygen) will be forced in as the inlet manifold pressure increases. The presence of additional air mass in the cylinder makes it possible to create a bigger explosion if more fuel is injected, increasing the power and torque output of the engine
conclusion
As we know that a turbocharger also performs the same work as the above using the engine exhaust gas but due its low efficiency in 4-stroke single cylinder engines the above process has been introduced.