Hybrid powertrains that use compressed air to help power a vehicle could dramatically improve the fuel economy, particularly in cities and urban areas where the traffic conditions involve a lot of starts and stops. In such conditions, a large amount of fuel is needed to accelerate the vehicle, and much of this is converted to heat in brake friction during decelerations. Capturing, storing and reusing this braking energy to produce additional power can therefore improve fuel efficiency. In this study, three approaches towards air hybrid powertrains are proposed and analyzed. In the first approach, an energy recovery valve or two shut-off valves connected to a convenient access hole on the engine cylinder is proposed to enable the cylinder to operate as a regenerative compressor and/or expander when required. In the second approach, one of the exhaust valves in an engine equipped with a Fully Variable Valve Actuation (FVVA) system is pneumatically or hydraulically operated as a dedicated gas transfer valve connected to an air reservoir. The third approach combines the advantages of the conventional valvetrain’s simplicity with emerging production technologies. In order to achieve this, two well established technologies are used in addition to valve deactivation; Variable Valve Timing (VVT) and/or Cam Profile Switching (CPS). Provided that a conventional, camshaft-operated variable valvetrain is used, the need of adopting fully variable valve actuation is eliminated and thus only minor modifications to the engine architecture are required. The aforementioned concepts are described in details. Some basic principles of their operation are also discussed in order to provide a better understanding on how fuel economy is achieved by means of engine hybridization and regenerative braking. Both experimental and computational results are presented and compared. Finally, a vehicle and driveline model, which simulates the operation of a typical passenger vehicle in urban driving conditions and predicts the efficiency of the energy regeneration, has been set up and used to study the effects of the application of each air hybrid concept on the vehicle’s energy usage throughout the New European Driving Cycle (NEDC) and the 10-15 driving cycle. The results have shown that each concept involves the optimization of valve timing for the best regenerative energy recovery and its subsequent usage. For the modelled vehicle, it has been shown that any of the three concept engines is capable of providing more braking power than needed during every deceleration and braking process, especially throughout the urban driving part of each cycle. The recovered braking energy in the form of compressed air has proved to be always sufficient to start the engine, if stop-and-start engine operation strategy is to be adopted.

É esperado que o consumidor, no momento de decidir qual carro ele irá adquirir, leve em conta, entre diversos outros fatores, a eficiência energética do modelo. Contudo, diversos trabalhos apontam que o consumidor subvaloriza o gasto total que terá com combustível no momento que decide qual modelo de carro irá comprar. Como carros são grandes produtores de externalidades, e por isso, frequentemente são objetos de política pública, é necessário entender esse comportamento do consumidor para que os formuladores o possam levar em conta no momento de fazer as políticas públicas. O objetivo principal desse trabalho ´e estimar o peso relativo que o consumidor brasileiro dá à economia de combustível no momento da escolha da compra do carro, e verificar se, de fato, há uma subvalorização da importância do gasto com combustível no mercado de carros novos no Brasil. Para tentar responder a pergunta proposta serão utilizados duas metodologias distintas. A primeira será uma regressão de preços hedônicos, e a segunda um modelo de demanda aninhado. / It is expected that the consumer, in the moment when deciding which car he will buy, take in account the energetic efficiency of the model. However, many works show that the consumer undervalues the total spent that he will have with fuel in the moment he decides which model to buy. Cars are important externalities creators, and so, are frequently target of public policies, it is necessary to understand this behave of the consumer in order that the policies makers can design the most useful policy. The main objective of this work is to estimate the relative weight that the Brazilian consumer gives to the fuel economy in the moment of the car purchase choice, and verify if indeed, there is a undervaluation of the weight of the fuel spending in the Brazilian new car market. To try to answer this question will be used two different methodologies. The first one is a hedonic prices regression, and the second a nested demand model.

In the face of the internationally tightened requirements and regulations for CO2 emissions from the transportation sector, waste heat recovery using a thermoelectric generator (TEG) has become the most significant research interest. A vehicular TEG, converting otherwise wasted thermal energy from engines to electricity directly for use in the vehicle systems, is a promising approach for vehicle original equipment manufacturers (OEMs) to reduce fuel consumption and lower CO2 emissions. This thesis aims to explore the main challenges to be faced in the commercialization of TEGs. Based on a review of the literature, four research gaps have been identified, which are respectively: * Translating the material improvements into TEG Performance, * Transient behaviors of vehicular TEGs under driving cycles, * Fuel saving percentage and cost-benefit estimation of TEG, * Bidirectional characteristic of TEM and bifunctional vehicular TEG. To directly address these research gaps, a quasi-static TEM model, a dynamic TEG model, a semi-empirical vehicular TEG model, and a dual-model TEM model have been respectively developed and validated through experiments on both TEM test rigs and TEG engine test benches. These developed models are used as tools to investigate the performance of TEG, parameters sensitivity, and integration effects. Model-based TEG control, TEG cost benefit ratio and feasibility of a bifunctional TEG are also explored based on the developed models. The simulation results show that TEG power generation is highly sensitive to the heat transfer coefficient of hot side heat exchanger and thermal contact resistance. The TEG installation position is identified as the most important integration effect. It has been found by the simulation result that the fuel saving with TEG installed upstream of the three-way catalyst (TWC) is 50% higher than the fuel saving with TEG installed downstream of the TWC. The fuel saving percentage for a skutterudite vehicular TEG, which can generate around 400-600W in constant speed 120km/h, is 0.5-3.6% depending on the integration position in the exhaust line. A 3-minute faster warm-up effect of engine oil can be obtained when the bifunctional TEG works in engine warm-up mode with electrical current applied.

Performance of two different waste heat recovery systems (one based on Rankine cycle and the other one using thermoelectricity) combined with non-hybrid, mild-hybrid and full hybrid systems are investigated. The vehicle under investigation was a 440hp Scania truck, loaded by 40 tons. Input data included logged data from a long haulage drive test in Sweden.All systems (waste heat recovery as well as hybrid) are implemented and simulated in Matlab/Simulink. Almost all systems are modeled using measured data or performance curves provided by one manufacturer. For Rankine system results from another investigation were used.Regardless of practical issues in implementing systems, reduction in fuel consumption for six different combination of waste heat recovery systems and hybrid systems with different degrees of hybridization are calculated. In general Rankine cycle shows a better performance. However, due to improvements achieved in laboratories, thermoelectricity could also be an option in future.This study focuses on “system” point of view and therefore high precision calculations is not included. However it can be useful in making decisions for further investigations.

A rear loading refuse truck was simulated with a conventional and hydraulic hybrid configuration. Models for the hydraulic hybrid components were developed to simulate the system. A control algorithm was developed using a stochastic dynamic programming approach. The results did not match those that are advertised by the commercially available systems, but reasons for this deviation are discussed. The predicted improvement in fuel economy ranged from 1% to 15% depending on variance in drive cycle and vehicle weight. A brief analysis of the cost of the hybrid system was also conducted based on an estimated drive cycle. This analysis showed that, at current fuel prices of about $4.00/gallon, the system may not make financial sense for a 10 year period of ownership. / text

É esperado que o consumidor, no momento de decidir qual carro ele irá adquirir, leve em conta, entre diversos outros fatores, a eficiência energética do modelo. Contudo, diversos trabalhos apontam que o consumidor subvaloriza o gasto total que terá com combustível no momento que decide qual modelo de carro irá comprar. Como carros são grandes produtores de externalidades, e por isso, frequentemente são objetos de política pública, é necessário entender esse comportamento do consumidor para que os formuladores o possam levar em conta no momento de fazer as políticas públicas. O objetivo principal desse trabalho ´e estimar o peso relativo que o consumidor brasileiro dá à economia de combustível no momento da escolha da compra do carro, e verificar se, de fato, há uma subvalorização da importância do gasto com combustível no mercado de carros novos no Brasil. Para tentar responder a pergunta proposta serão utilizados duas metodologias distintas. A primeira será uma regressão de preços hedônicos, e a segunda um modelo de demanda aninhado. / It is expected that the consumer, in the moment when deciding which car he will buy, take in account the energetic efficiency of the model. However, many works show that the consumer undervalues the total spent that he will have with fuel in the moment he decides which model to buy. Cars are important externalities creators, and so, are frequently target of public policies, it is necessary to understand this behave of the consumer in order that the policies makers can design the most useful policy. The main objective of this work is to estimate the relative weight that the Brazilian consumer gives to the fuel economy in the moment of the car purchase choice, and verify if indeed, there is a undervaluation of the weight of the fuel spending in the Brazilian new car market. To try to answer this question will be used two different methodologies. The first one is a hedonic prices regression, and the second a nested demand model.

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