Emissions reduction potential by coupling a thermoelectric generator to an exhaust heater in heavy duty vehicles
- Autores: Joan Ximinis Tarrés
- Directores de la Tesis: Albert Massaguer (dir. tes.), Eduard Massaguer Colomer (codir. tes.), Antoni Pujol Sagaró (tut. tes.)
- Lectura: En la Universitat de Girona ( España ) en 2022
- Idioma: inglés
- Tribunal Calificador de la Tesis: Andreu Cabot Codina (presid.), Josep Ramón González Castro (secret.), Ana Inés Fernández Renna (voc.)
- Programa de doctorado: Programa de Doctorado en Tecnología por la Universidad de Girona
- Materias:
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- Resumen
In the European Union, about 70% of pollution emissions come from road transportation. This fact is the main cause of air pollution within urban areas while Governments around the world are focusing their efforts to improve air quality stablishing low emission zones. These policies can improve air quality in some capitals or cities highly populated but in global terms, commercial transportation is far from substituting Internal Combustion Engines (ICE) as the main propulsion system, specially for Heavy-Duty Vehicles (HDV).
Combustion engines produce great quantities of heat energy during their working process. Around two thirds of this thermal energy is lost as residual heat, with 40% of this loss transformed in exhaust gases emitted to the atmosphere. Apart from being a contributor to global warming, this residual heat could be transformed in a more usable energy by a thermoelectric principle.
Thermoelectric applications are diverse and specialized in many science fields such as refrigeration in solid state (Peltier effect) and energy conversion from thermal to electric (Seebeck Effect). The application of Thermoelectric modules (TEM) is specially interesting in terms of wasted energy recovery. This work is an applied example of thermal wasted energy recovered and used afterwards to increase the efficiency of a standard Aftertreatment System (ATS).
Our modest point of view and contribution to reduce environmental impact is related to a validation of an energetically closed system to ensure a better performance of the standard ATS in a diesel-powered EURO VI Heavy duty vehicles (HDV) currently circulating in our roads and highways. Nowadays Selective Catalytic Reduction systems (SCR) starts performing with exhaust gas temperatures higher than 180°C. Our research is focused on shortening the inactive time of the standard system in order to improve pollutant emissions mainly in low engine regime routes and cold start conditions.
First part of this research is focused in validating the Exhaust Gas Heater (EGH) viability in reducing NOx emissions without negative effects in a standard exhaust gas circuit. Experimentation was held using a HDV Euro VI vehicle in a certified rolling bench. Results are encouraging but the system has to be properly adapted and optimized. We are seeking a balance between NOx abatement and thermal wasted energy harvested for increasing exhaust gas temperature.
Second part of this study explores the Automotive Thermoelectric Generator (ATEG) viability as the only source of energy to power the EGH. It quantifies the electrical energy produced in three common engine regimes (1000, 1250 and 1500 rpm). It measures production variations affected by different Full Throttle Pedal Positions (FTPP) all along the exposed regimes.
This study presents a Thermoelectric Aftertreatment Heater (TATH) as a solution coupled to the vehicle standard configuration. It also determines the ideal location of both EGH and ATEG to optimize its performance and keep the standard ATS with minimal variations. The use of this system is divided into two different phases, heating stage and recovery stage. Heating stage is when EGH consumes electricity to rise exhaust gas temperature. On the other hand, recovery stage is applied when exhaust gas temperatures are high enough to allow ATEG recover wasted energy. Parameters such as backpressure and added weight has been taken into account in order to provide a fair energy balance to the comparison. In this regard, extra fuel consumption of the HDV has been quantified.
Third part of our research explores the different HDV routines and its particularities in order to determine in which ones the TATH can provide a major NOx improvement. The effects of this system are explored in a real transportation routine of a long-haul journey. The presented system is reducing polluting emissions in low engine regime circumstances, mainly in urban areas that are populated. Recovery stage of the system is quantified within this specific routine. Afterwards, the amount of energy required for heating stage is quantified concerning routine requirements.
Finally, experimental results demonstrate that a certified EURO VI HDV can produce NOx emissions 5 times above the standard limit value under specific circumstances (low-speed regimes). The accomplishment of current EURO VI and prospective EURO VII has been analyzed taking into account the benefits of this proposed TATH compared to the standard homologated ATS of this particular vehicle. Results demonstrate a NOx reduction up to 97.2% using the system proposed into this particular mission profile. Apart from that, it is also demonstrated that the ATEG can produce the energy required by the EGH in a long-haul mission profile. However, the added weight and the back pressure caused by the TATH is expected to increase the fuel consumption of the vehicle in 0.35%.
