# Strategies for Reducing Automobile Fuel Consumption
## 3 Vehicle Design and Technology
### Advances in Internal Combustion Engines (ICEs)
However, when the engine restarts (i.e., transient state), fuel consumption briefly increases above the reference at a specific operating temperature. This increase occurs because the generator is activated to compensate for the battery charge lost during engine startup. The overall benefit of the start-stop system is determined by balancing the energy saved during zero-speed operation and the energy required for engine restart. The final outcome depends on factors such as the duration of idleness in each cycle, the engine's consumption rate during idleness, the additional energy needed to start the engine, and the specific strategy employed by the generator during operation. These factors account for variations in fuel consumption between different vehicles and driving cycles [31]. The landscape of vehicle _powertrain technologies_ is undergoing a transformative shift in response to the stringent CO2 and fuel economy regulations set beyond 2020. Conventional powertrains and fuels alone are no longer sufficient to meet these everchanging standards. This fact has catalyzed an increasing diversification of powertrain technologies and energy carriers, highlighting _engine rightsizing_ as a pivotal strategy for both conventional vehicles (i.e., powered by ICEs) and electric vehicles (EVs). Integral to this change is the integration of Connected Powertrains and Advanced Driver Assistance Systems (ADASa). These technologies are becoming increasingly prevalent in vehicle designs, offering significant improvements in fuel consumption, safety, and comfort. The development of these systems requires a comprehensive full life-cycle methodology, fostering the advancement of new engine technologies, sensors, and on-board computing. These innovations are central in enabling real-world implementations of high-efficiency engine technologies, like low-temperature combustion and high-speed controls. A prominent example of such advancements is the _SuperTruck II program_ (by Cummins), recognized by the U.S. Department of Energy (DoE) for its pioneering research in heavy-duty diesel engine technology. It achieves a milestone of 55% _brake thermal efficiency_ (BTE), which is the power taken by the engine crankshaft out of the total power generated by the ICE, through the integration of waste heat recovery systems. This initiative underscores the synergy between hardware optimization and sophisticated engine calibration. The SuperTruck II program (an extension of the SuperTruck I initiative) aims to further double efficiency and halve CO2 emissions, contributing significantly to global energy savings. A study by [PERSON] et al. [32] investigated the effects of reducing vehicle weight (i.e., lightweighting) on fuel efficiency and cost for different powertrains: conventional gasoline vehicles, hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (EVs). Using the _FASTSim tool_, the study found that lightweighting has the most significant impact on conventional vehicles, reducing fuel consumption by about 0.58 L/100 km for a 150 kg mass reduction. While the impact on HEVs, PHEVs, and EVs is less pronounced in terms of fuel efficiency, lightweighting considerably reduces battery costs, particularly for PHEVs and EVs. The study concluded that the lightweighting practice is cost-effective only when it costs less than USD 6 for each kg of mass reduced and emphasizes its importance in lowering both component and fuel costs. The work of [PERSON] et al. [18] focused on improving thermal efficiency and reducing carbon emissions in ICEs. It reviewed advanced strategies for higher efficiency and cleaner combustion, considering thermodynamic cycles, gas exchange systems, advanced combustion strategies, and thermal and energy management. This study discusses the challenges in these modules and suggests integrating different technologies, like hybrid thermal cycles and variable intake systems, into powertrains with advanced electrification and artificial intelligence.