# Strategies for Reducing Automobile Fuel Consumption
## 3 Vehicle Design and Technology
### Advances in Internal Combustion Engines (ICEs)  
Over the decades, technological innovations have substantially increased ICE efficiency. Contemporary high-power, low-speed diesel engines present efficiency values of up to 50% [18]. Notwithstanding these advances, many opportunities remain to refine ICE systems. Prospective advancements for diesel and gasoline engines, projected to decrease passenger cars' fuel consumption by approximately 20% within the next decade, incorporate strategies such as friction reduction, enhanced compression ratios, comprehensive variable valve control, two-stage turbochargers, cylinder deactivation, direct fuel injection, accessory electrification, start/stop system integration, refined transmission systems, and reductions in vehicle weight, tire resistance, friction, and aerodynamic drag [19]. Such evolution in ICE technologies and vehicular architecture holds significant promise for augmented fuel efficiency and a diminished ecological footprint. Recent advancements in gasoline engine _combustion paradigms_ comprise [20] Compression Ignition (GCI), Homogeneous Charge Compression Ignition (HCCI), Partially Premixed Combustion (PPC), Low-Temperature Combustion (LTC), Octane-on-Demand (OOD), and Reactivity-Controlled Compression Ignition (RCCI). Such combustion paradigms have effectively and positively transformed contemporary engine efficiencies. Their distinctiveness lies in their unique fuel-air mixture preparation and their reliance on varying degrees of flameless combustion. Additionally, combustion strategies often combine technologies such as High-Pressure Direct Injection (HPDI), Cyclical Multi-Injection (CMI), Extensive Exhaust Gas Recirculation (EEGR), and Adaptive Valve Timing (AVT). Contemporary gasoline engines have been optimized to operate at elevated _compression ratios_, consequently increasing engine efficiency and reducing emission levels. Moreover, high compression ratios in compression ignition engines fueled with gasoline also help increase efficiency. Nevertheless, the attainment of such efficiencies typically requires the concurrent evolution of fuel formulations and engine designs, which underscores the importance of developing fuels and engines simultaneously. Some modern innovations in engine technology include turbocharged _gasoline direct injection compression ignition_ (GDCI) engines, which have notably delivered a 22% reduction in fuel consumption [16; 21]. The use of _gasoline direct injection_ (GDI) engines, supported by _lean combustion techniques_, might contribute to enhancements in fuel economy up to 15%. Furthermore, other _super-lean combustion technologies_ are projected to reach thermal efficiency values of up to 45%. When subjected to _increased injection pressures_, diesel engines exhibit enhanced fuel atomization, promoting improved air-fuel mixing, which subsequently increases the engine's efficiency [22]. Thermal efficiency values up to 52.9% are being obtained in heavy-duty diesel engines, with improvements such as (approximately) 2% reductions in gas exchange losses, a 0.9% reduction in frictional losses, and a 0.6% reduction in accessory consumption. Concurrently, additional efforts are directed toward energy recovery: up to 2.5% from exhaust gases, and up to 1.3% from the thermal energy of the coolant. These endeavors support energy recovery systems that are based on the organic Rankine cycle (ORC) and incorporate advanced methodologies like _turbocompounding_[23], which produces work (or generates electricity) by utilizing the exhaust gas energy by means of a gas turbine, mirroring a _cogeneration_ approach [24; 25]. _Energy recovery_ via complementary thermodynamic _bottoming cycles_ presents an important resource for increasing the fuel efficiency of ICEs. Such cycles encompass the following: (a) Organic Rankine Cycle, (b) Kalina Cycle, (c) Trilateral Flash Cycles, (d) Supercritical CO\({}_{2}\) Rankine Cycle, and (e) Gas-based Stirling and Brayton Cycles.