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Toyota Motor Corporation has developed a dedicated compressed natural gas (CNG) powered vehicle “Camry” sedan to achieve near zero emissions and to meet rising demand for alternative fuel. A new engine that uses CNG as fuel has been developed by modifying the base 2.2 liter gasoline engine. In the unmodified base engine, torque and power for CNG decrease compared to gasoline. The new engine has adopted a high compression ratio, intake valves with early closed timing, intake and exhaust valves with increased lift and a low back pressure muffler, which thereby restored the loss of engine power. In order to greatly reduce exhaust emissions, a multi port injection system was chosen, and the injectors and pressure regulator have been newly developed. At the same time, precise A/F ratio control and special catalysts for CNG exhaust gas have been utilized. The resulting CNG engine output power has been restored to nearly that of the gasoline base engine, and it was found that CNG system has the possibility to meet the California SULEV exhaust emission standards which were adopted in November 1998.
Kato et al. (Mon,) studied this question.