# Strategies for Reducing Automobile Fuel Consumption
## 3 Vehicle Design and Technology
### Advances in Alternatives to Petroleum-Based Fuels  
In the field of ICEs, traditionally powered by fuels such as gasoil (i.e., diesel) and gasoline (i.e., petrol), recent studies have highlighted the potential of the use of diverse alternative fuels. _Hydrogen_ stands out for its high energy efficiency and clean combustion, emitting only water vapor, but faces challenges in efficient storage and sustainable production methods. Other fuels like _bio fuels_ (biodiesel and bioethanol) offer sustainability and lower emissions, despite the fact that their production can impact food resources and land use. _Natural gas_, with its cleaner burn compared to traditional fuels, struggles with storage and refueling infrastructure. _Synthetic fuels_ (e-fuels), compatible with existing ICEs and infrastructure, are hindered by high production costs and energy-intensive manufacturing. Each fuel presents a unique set of advantages and challenges, indicating that a multi-faceted approach is required for sustainable transportation solutions. [PERSON] et al. [34] showed the effectiveness of the use of simarouba glauc biodiesel in a diesel engine for improving brake thermal efficiency and reducing emissions of carbon monoxide (CO), hydrocarbon (HC), and smoke opacity, especially when combined with exhaust gas recirculation (EGR). A study by [PERSON] et al. [35] investigated the performance of a diesel engine using biodiesel derived from cashew nut shell liquid, augmented with hydrogen and ethanol. This combination was found to significantly boost brake thermal efficiency and reduce CO and HC emissions, suggesting a promising pathway for reducing diesel engine pollution [35]. _Hydrogen_'s unique combustion characteristics are being harnessed to develop reduced-emissions spark-ignition engines, with dynamic performances comparable to that of conventional gasoline engines but achieving efficiencies comparable to that of diesel engines. Hydrogen's particular properties, such as low flammability limit and high flame speed, promote stable combustion in spark-ignition engines, resulting in reduced NOx formation. This characteristic enables efficient engine operation, particularly at low- and medium-torque regimes. Innovative engine design improvements (e.g., increased combustion pressure and engine downsizing) further enhance the efficiency and power densities of hydrogen-fueled engines, surpassing those of conventional hydrocarbon-fueled engines [36]. [PERSON] et al. [37,38] investigated the impact of hydrogen blending with gasoline in spark-ignition engines, indicating that a 20% hydrogen blend can improve engine efficiency and reduce emissions. While such blending has been shown to reduce HC and CO emissions, contributing to improved combustion efficiency, it is also associated with an increase in nitrogen oxide (NOx) emissions. Collectively, these studies illuminate the potential of biofuels and hydrogen blends in transitioning toward more sustainable and efficient internal combustion engine technologies. While alternative fuels like hydrogen present promising benefits in terms of efficiency and reduced certain emissions, they necessitate careful management and further technological innovation to mitigate trade-offs, particularly concerning increased nitrogen oxide emissions. In investigating the performance of hydrogen/diesel reactivity-controlled compression ignition (H\({}_{2}\)/diesel RCCI) engines, a study by [PERSON] et al. [39] reveals that the _indicated thermal efficiency_ (ITE) is significantly enhanced by employing a _double direct injection_ (DDI) strategy over a _single direct injection_ (DI) strategy, primarily due to improved fuel distribution and combustion conditions. The ITE increases notably when intake pressure is raised from approximately 100 to 120 kPa but decreases with further pressure enlargements due to reduced combustion efficiency and higher combustion temperatures.