Feasibility of using Thermoelectric Generators to Improve Fuel Efficiency in Existing In-service Vehicles

O'Keeffe, Myles E. (2022) Feasibility of using Thermoelectric Generators to Improve Fuel Efficiency in Existing In-service Vehicles. [USQ Project]

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Climate change is defined as the “long-term shifts in temperatures and weather patterns” (United Nations 2020). While climate change occurs naturally, this process has been significantly accelerated by human activities since the 1800s. This acceleration is largely due to the consumption of fossil fuels such as coal, oil and gas resulting in Greenhouse Gas (GHG) emissions. Globally, Australia is one of the largest contributors of GHG emissions per capita, largely due to the relatively low population density of Australia when compared to other countries.

Within Australia, the transport sector is responsible for 17.6% of total emissions with road transport making up 85% of that value. In an effort to reduce these emissions, manufacturers are required to meet higher fuel efficiency standards for all new vehicles. Unfortunately, this also means that once a vehicle is purchased by a consumer it no longer receives improvements to its fuel economy. With over 20 million vehicles concurrently registered (with this number increasing each year), the existing fleet represents a significant opportunity to reduce emissions.

This aims and objectives of this project is to identify the feasibility of using thermoelectric generators to improve fuel efficiency in existing in-service vehicles. According to the Seebeck Effect, thermoelectric generators produce a voltage differential when subjected to a temperature gradient. The main working principle behind this method of improving fuel economy is to convert a portion of the waste heat energy to electricity, then to use this electricity to supplement the vehicles electrical system. This reduces the demand on the alternator which is mechanically powered from the crankshaft, thus reducing the parasitic losses on the engine. This ultimately improves fuel economy. The main condition that such a device would need to satisfy is a cost to performance metric where the reduction in running costs is enough to offset the original investment cost within a few years.

While there have been previous attempts at utilising thermoelectric generators for this purpose, these attempts have not yet been deemed viable due to the focus on new vehicles where the electrical demand is much higher. Older vehicles often feature far less electronics with a subsequent lower electrical demand.

Research was performed in regards to the various strategies to implement TEGs while obtaining preliminary data from the test vehicle. Findings from the research and parameters from the vehicle were then used to determine a suitable TEG module that displayed the highest return per cost. Once a module was selected, a unit was designed and constructed that was largely dependent on the physically available space. The theoretical maximum output for this unit was 48 watts.

Results from testing were initially lower than expected, producing 7 watts at 3500 RPM (100 km/h) however, after analysis multiple factors were identified that contributed to these results. The two main factors responsible for this was the utilisation of static testing vs dynamic testing and underperforming TEG modules. Without expensive equipment, a static testing method was unable to adequately load the engine leading to significantly less heat output. Spare modules were later tested under known conditions and were found to be under preforming when compared to their specification datasheet. Analysing the results while accounting for this reduced performance found the module array to be 88.5% efficient with the losses attributed to minor temperature deviations between the modules and resistances in the wiring connectors.

Calculating the impact on fuel consumption while making various assumptions yielded a fuel economy improvement of 0.16% or an average saving of 1.57 L per year. If the unit were to be producing its maximum output, then these values became 1.10% and 10.82 L respectively. These values of improvement were calculated while assuming no additional weight was added to the vehicle when installing the unit. In practice the unit added 7.3 kg when replacing the original exhaust section. Re-calculating the impact on fuel economy when accounting for this change in mass yielded a 0.11 % increase in consumption or an additional 1.06 L consumed per year at 7 watts of output while, at maximum output these values became a reduction of 0.83 % or a reduction of 8.19 L per year.

If this were to be implemented on a large scale in Australia alone, there is the potential to reduce the yearly consumption by 10.82 million L with a 5% adoption rate assuming each unit achieves its maximum output. With unleaded fuel valued at approximately $2.00 per L, this represents a potential cost saving of $21,640,000 AUD per year. A cost breakdown of the device revealed the supporting components such as thermal paste, wiring, insulation etc, attributed to 42.32 % of the total cost far outweighing the modules or heatsink at 18.08 % and 26.02 % respectively (main body was 13.56%). With the total cost of the unit at $411.33, even at maximum output, it would require approximately 25 years before the savings would outweigh the original investment cost making this device unfeasible.

Given the poor performance to weight ratio as well as the poor performance to cost ratio of a completed thermoelectric generator device, this strategy of improving fuel economy is not feasible with the current level of thermoelectric generator modules.

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Item Type: USQ Project
Item Status: Live Archive
Faculty/School / Institute/Centre: Current – Faculty of Health, Engineering and Sciences - School of Engineering (1 Jan 2022 -)
Supervisors: Wandel, Andrew; Ahfock, Tony
Qualification: Bachelor of Engineering (Honours) (Mechanical Engineering)
Date Deposited: 20 Jun 2023 03:04
Last Modified: 20 Jun 2023 03:04
Uncontrolled Keywords: fuel efficiency; emissions; thermoelectric generators
URI: http://sear.unisq.edu.au/id/eprint/51898

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