Hollywood's annual sci-fi disaster film "2012" has been released worldwide. The film tells us that the deteriorating global ecological environment has finally ushered in the end of the world. Environmental deterioration is the most important issue facing humanity in the 21st century. The destruction of traditional energy for the environment and the shortage of traditional energy will directly affect the sustainable development of human society and threaten human health and living environment. Therefore, finding and developing new energy sources and alternative energy sources have extremely important significance for the entire human society.
As a large energy consumer, the energy conservation and emission reduction of the automotive industry has always been one of the most important issues of concern to governments of all countries. At present, the global alternative energy sources with abundant resources and mature technologies are gas fuels. However, the use of gaseous fuels in automobiles can sometimes cause environmental pollution due to technical defects. In October 2009, the deputies of the Guangzhou Municipal People’s Congress questioned the environmental protection of LPG buses in Guangzhou and triggered a series of arguments and counterarguments. In this incident, there is a close and direct link between the controversial core components and energy-saving and emission reduction, which is the gas engine to the conversion of gas fuel to power energy.
Gas engine environmental protection advantages
Currently, engines that use a single-gas fuel as a source of power mainly include LNG (liquefied natural gas) engines, CNG (compressed natural gas) engines, and LPG (liquefied petroleum gas) engines. Compared with diesel engines with the same displacement, the gas engine is quite dynamic and has obvious environmental advantages. It is easier to achieve national IV and national V emissions. And the current production technology tends to be mature, and the production process equipment and diesel engine can be used universally. Under the premise of maintaining the oil price difference, the fuel economy is significant. However, gas engines also have certain defects, such as short driving range, long fuel refueling time, and too much investment in gas station construction.
Since the environmental protection advantages are obvious, why does the Guangzhou Municipality have controversies over the LPG bus pollution incident? In fact, many experts have already given answers to the October 2009 incident, saying that the problem is that there is no comparability between the “irreconcilable tests†that caused controversy. It's as if the "fast-tipping cars are definitely better than the new low-end vehicles." Compared with the good operating conditions of LPG buses in Hong Kong, it can be found that the emissions of original LPG buses and modified LPG buses are significantly different. This may be the Guangzhou LPG. The real cause of public transport pollution incidents.
At present, China's bus industry has achieved remarkable results in the use of clean fuel for gaseous fuels. Bus companies in Beijing, Shanghai, Guangdong, Sichuan, Chongqing, Hainan and Gansu have already taken a solid foundation in the development of environmentally friendly and energy-saving gas city buses. With the completion and commissioning of China's "West-East Gas Pipeline" pipeline network, the supply of foreign gas sources has steadily increased, and gas-fueled passenger cars have ushered in the peak period of development. In recent years, the holding of major events in China has not been possible without the gas fuel clean energy bus. From the 2008 Olympic Games to the 2010 Guangzhou Asian Games and the Shanghai World Expo, the participation of gas clean energy fuel buses has already been or is about to take place.
The mainstream engine manufacturers at home and abroad are seeing this situation. They have introduced passenger car gas engines with environmental protection and energy saving technologies, such as YC6M, YC6L, YC6G, and YC4F, which have been listed on the market in recent years. Natural gas engines, internationally renowned engine manufacturers such as Cummins, Iveco, and Daimler-Chrysler are also making every effort to develop and promote gas engines. It can be said that buses equipped with gas engines have become an indispensable part of major cities, and they are increasingly becoming the mainstream of urban public transport buses.
Gas engine development status
China began to develop low-pressure natural gas vehicles in the 1950s. After the reform and opening up in the mid to late 1980s, the development and application of gas-fueled vehicles accelerated. Domestic large-scale engine factories and automobile factories such as Yuchai, Shangchai, Weichai, Dongfeng and Liberation have successively introduced their respective gas engine products to be used in the market. In 1988, China imported equipment from CNG refueling stations, refitted auto parts and high-pressure cylinders from Australia, New Zealand, and Canada, and established stations in Nanchong and Daqing respectively, opening a new era for the development of CNG vehicles.
Compared with LNG engines, CNG engines and LPG engines are more technologically mature and economically cost-effective. Currently, CNG engines have been widely used in their third-generation electronically-controlled CNG injection technology. They use high-pressure injection, through throttle sensors, and gas flow. Sensors, speed sensors, water temperature sensors, intake air temperature sensors, pressure sensors, and oxygen sensors, etc., are controlled by the central processing unit to control the ignition, the air-fuel ratio, and the like. The more advanced LNG in-cylinder direct injection technology has been tested in small batches at present, and its power, economy, and emissions are excellent. However, it is difficult to develop, expensive, and costly. Domestic development has not yet begun.
Compared with conventional diesel engines, the gas engine eliminates parts related to the fuel injection system of the original diesel engine, and adds components such as a vapor pressure regulator (LPG engine) and a pressure reducer (CNG engine) that supply gaseous fuel. The conventional diesel engine is a compression ignition engine, and the gas engine adopts the same ignition method as the gasoline engine because of its limited fuel characteristics (anti-knocking performance). After the injector was cancelled, the injector hole on the original cylinder head was changed to the spark plug hole. After the oil pump is cancelled, an ignition gear is mounted on the crude oil pump installation position, and the ignition timing signal of the engine is obtained through the ignition timing sensor. Added ignition system consisting of ignition module, ignition coil and spark plug.
The control system of the gas engine is mostly electronically controlled. Compared with the mechanical diesel engine, the air-fuel ratio, ignition advance angle, and boost pressure of each operating point achieve more precise and more scientific control. To meet these control requirements, sensors such as MAP, MAT, ECT, ignition timing, and oxygen concentration were added.
Due to the adjustment of China's energy strategy structure, more gas fuel resources will be imported for domestic use in the future. The cities currently implementing LNG refueling systems in China are Beijing, Urumqi, and Changsha. Nearly a hundred LNG single fuel bus demonstration vehicles are in operation. CNG vehicles have been promoted in Sichuan, Chongqing, Beijing, Xi’an, Inner Mongolia and other places. LPG environmental and energy-saving gas city buses have also been piloted in public transport systems in Beijing, Shanghai, Guangdong, Sichuan, Chongqing, Hainan and Gansu. In foreign countries, LPG has been used as fuel for light vehicles for many years.
Gas engine development prospects
The electronic control system of the gas engine is different from that of the traditional diesel engine electronic control system. There are special requirements for the boosting and post-processing, and the advanced electronically controlled fuel injection technology is applied to the gas engine so that the engine temperature, load, and speed can be used. Key parameters such as gas fuel supply, mixture concentration, and ignition timing are precisely controlled to increase engine power and reduce exhaust pollution. Air-fuel ratio control is very effective in the application of electronically controlled fuel injection engines. It adjusts the air-fuel ratio in real time by monitoring engine emissions, and achieves optimal economy and emissions through high-energy, precision-ignition, and other automated coordination and optimization methods. From the cost point of view, the cost of the gas engine electronic control system is still slightly lower than the diesel electronic control system. Therefore, the potential for in-depth development of electronic control systems is enormous, and there will be better development in the future.
Due to Euro IV emission regulations, it is not only required to limit the emission of natural gas engines for non-methane hydrocarbons (NMHC), but also to control total hydrocarbon emissions (THC). However, how advanced oxidation type post-processing technology is successfully applied to gas engines is also one of the key technologies and has great research value. The relevant experts of the LPG bus pollution in Guangzhou also pointed out that it is related to its exhaust gas aftertreatment system.
At present, the infrastructure and related parts and components industries of domestic gas fuel passenger cars are not yet perfect, users still feel the mystery about the gas engine electronic control technology, and they are skeptical about domestic electronically controlled gas engines. The developed cities represented by Beijing and Shanghai mainly use imported gas engines. In recent years, domestic gas engines have not only achieved widening in the matching power range, but also have breakthroughs in the supporting fields, and the failure rate of repair during operation has also been greatly reduced. Domestic diesel engine factories represented by the above-mentioned diesel, Yuchai, Weichai, etc. continue to develop new technologies and new models, represent the technical strength of the Chinese internal combustion engine industry, and represent the development direction of China's future power.
In addition, the development of gas-fueled buses has important implications for reducing exhaust pollution and saving petroleum resources. China's relatively abundant natural gas and liquefied petroleum gas resources also provide strong energy security for the promotion and application of gas-fueled buses and gases. The cost of using fuel is clearly competitive with rising oil prices and should be accepted by more bus users. The gas engine is a new type of green power in the 21st century. The future city will surely have its own appearance due to its appearance. The development and production of high-efficiency, low-pollution gas engines will be the future direction of the bus industry in China and even the world.
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