Power and Fuel Economy of a Radial Automotive Thermoelectric Generator: Experimental and Numerical Studies

Abstract

Recent developments of high performance thermoelectric (TE) materials have increased the interest of using this technology to directly convert waste heat into electricity. In the automotive sector, many automotive thermoelectric generators (ATEGs) designs use TE modules (TEMs) with high hot side temperatures to cope with high engine load regimes. Here, we develop a new concept of a radial ATEG that is specifically designed to work with low temperature TEMs, which enables the use of Pb-free modules and reduces the thermal stress of the device. A prototype is built and tested at different regimes in an engine test bench. A numerical model of the ATEG is developed and validated. The consequences of modifying (1) the exchange area between the heat absorber and the exhaust gases and (2) the effective figure of merit of TEMs on the electrical output power and fuel economy are investigated by means of simulations. Results indicate that the maximum fuel economy (1.3%) is not attained at the point of maximum output power (228 W). In terms of fuel economy, the back pressure at the exhaust penalizes high mass flow regimes. We use a dimensionless parameter to analyze the potential of the ATEG for reducing fuel consumption.

Effects of Design Parameters on Fuel Economy and Output Power in an Automotive Thermoelectric Generator

“…The value of the convective heat transfer coefficient, h, multiplied by the exchange area, A, between the six inner cylindrical holes and the exhaust gas was calculated for different designs by varying the diameter D of the holes from 8 mm to 20 mm. Results with engine load operating conditions that gave the maximum P ATEG value in the laboratory experiment (case 6 in Table 3) V w = 580 L/h, as in Reference [7]) are shown in Figure 15a. The trend of hA as a function of D followed the same behavior as in Figure 13b.…”

“…In our ATEG, the heat absorber was a copper block with six cylindrical holes of 12 mm inner diameter (Figure 1). As pointed out by other authors, this type of geometry generates more back pressure than heat absorbers based on fins, for example, Reference [7]. However, heat exchangers with cylindrical holes have some advantages over fin heat absorbers since the latter have constraints related to the type of material being used and the geometrical dimensions of the fin (minimum available fin spacing and fin thickness depending on the manufacturing techniques).…”

“…To correctly reproduce the experimental conditions, simulations used water as the coolant and the product of a combustion reaction as the exhaust gases. The latter assumption better represented actual laboratory conditions than imposing air as exhaust gases, as commonly adopted in other numerical models of ATEGs [7,18]. A complete combustion reaction of diesel fuel with an air-fuel ratio (AFR) higher than that of stoichiometric conditions (AFR s ) was implemented and properties such as dynamical viscosity, thermal conductivity, specific heat, etc., as a function of the temperature of the mixed gas were used in the calculations.…”

Analysis of an automotive thermoelectric generator coupled to an electric exhaust heater to reduce NOx emissions in a Diesel-powered Euro VI Heavy Duty vehicle

“…This will avoid the need for the electric system to consume more fuel to produce the extra electrical energy. Many theoretical models [4] and experimental prototypes [5]- [7] have been developed which demonstrate the feasibility of automotive ATEGs. Other ways to produce this additional energy from exhaust gases may be the use of Organic Rankine Cycle (ORC).…”

Comparative analysis of numerical models of plate-fin heat sinks with forced convection for thermoelectric energy generation

“…This technology is currently applied to power autonomous sensors, electronic devices in off-grid remote areas, etc. Great efforts are dedicated to employ them as massive power generators in industrial processes with large amounts of waste heat [1]. However, the efficiency of a TEG system highly depends on the design of its heat transfer system.…”