**1. Discuss the Reasons Why Natural Gas Vehicles Are Safer than Gasoline Vehicles** In the realm of automotive safety, natural gas vehicles (NGVs) often outperform their gasoline counterparts. This superiority in safety can be attributed to several inherent properties of compressed natural gas (CNG) and the design considerations incorporated into NGVs. Firstly, natural gas possesses a significantly higher ignition point than gasoline. With an ignition point of over 650°C, CNG is much more difficult to ignite compared to gasoline, which has an ignition point of around 210°C. This high ignition threshold significantly reduces the risk of accidental fires in NGVs. Secondly, natural gas has a lower density than air, which means that any leaked gas will quickly dissipate into the atmosphere, reducing the chances of reaching a concentration sufficient for ignition. This diffusion-friendly property of CNG contrasts sharply with the volatile nature of gasoline, which can easily form explosive mixtures in confined spaces. Moreover, NGVs are equipped with sophisticated leak detection and shutdown systems. These systems are designed to rapidly detect any gas leaks and automatically shut down the vehicle's fuel supply, minimizing the risk of a dangerous situation developing. In addition, the clean-burning nature of natural gas results in fewer harmful emissions compared to gasoline, contributing to better air quality and reducing the risk of respiratory health issues for passengers and drivers. Lastly, the design and construction of NGVs, including reinforced fuel tanks and fire-resistant materials, also contribute to their overall safety. These features ensure that in the event of an accident, the risks associated with a fuel leak or fire are minimized. In summary, the high ignition point, low density, leak detection systems, clean-burning properties, and robust design of NGVs collectively contribute to their superior safety performance compared to gasoline vehicles. **2. Discussion on the Names and Working Principles of Three Types of Natural Gas Vehicle Powertrains in English** Natural gas vehicles (NGVs) employ various powertrains to harness the clean-burning energy of compressed natural gas (CNG). Three primary types of NGV powertrains are: **Spark Ignition Gasoline Engine (SIGE) Converted to Run on CNG** The most common type of NGV powertrain is the modified spark ignition gasoline engine (SIGE). These engines originally designed for gasoline are converted to run on CNG through modifications such as new fuel injectors, a gas mixer, and a CNG storage tank. The working principle remains largely the same as a gasoline engine, with the spark plug igniting the air-CNG mixture in the combustion chamber. However, the higher octane rating and cleaner combustion of CNG results in improved performance and reduced emissions. **Dedicated Natural Gas Engine (DNGE)** Dedicated natural gas engines (DNGEs) are specifically designed to run on CNG. These engines typically feature higher compression ratios and modified combustion chambers for improved combustion of CNG. The DNGE uses a spark plug to ignite the CNG-air mixture, similar to the SIGE converted engine. However, the dedicated design allows for optimized performance and durability when running on CNG. **Diesel Engine Converted to Run on Dual Fuel (Diesel-CNG)** Another type of NGV powertrain is the diesel engine converted to run on a dual fuel system. These engines can operate on both diesel and CNG, allowing for flexibility in fuel choice. The working principle involves the diesel injection system injecting a small amount of diesel to ignite the air-CNG mixture. This dual-fuel approach combines the torque and power of diesel with the environmental benefits of CNG. In conclusion, NGVs employ three primary types of powertrains: SIGE converted to run on CNG, dedicated natural gas engines (DNGEs), and diesel engines converted to run on dual fuel (diesel-CNG). Each powertrain type offers unique benefits, but all share the common goal of harnessing the clean-burning power of CNG for improved emissions and environmental performance.
