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Compared with petroleum fuel, liquefied petroleum gas (LPG) demonstrates advantages in low CO2 emission because of propane and butane, which are the main components of LPG, making H/C ratio higher. In addition, LPG is suitable for high efficient operation of a spark ignition (SI) engine due to its higher research octane number (RON). Because of these advantages, that is, diversity of energy source and reduction of CO2, in the past several years, LPG vehicles have widely used as the alternate to gasoline vehicles all over the world. Consequently, it is absolutely essential for the performance increase of LPG vehicles to comprehend the combustion characteristics of LPG and to obtain the guideline for engine design and calibration. In this study, an LPG-SI engine was built up by converting fuel supply system of an in-line 4-cylinder gasoline engine, which has 1997 cm3 displacement with MPI system, to LPG liquid fuel injection system [1].

Vehicles fueled by liquefied petroleum gas (LPG) are also required to provide high levels of engine torque and power, in addition to clean emissions for environmental friendliness, low fuel consumption and energy savings. In response to these demands, it can be expected that engine control performance and exhaust emissions can be substantially improved by controlling the fuel supply system with high accuracy. Energy savings along with higher levels of speed, accuracy and reliability can also be expected. The conventional method of controlling fuel supply systems has been to control the fuel injection pressure to a high level at all times under all engine operating conditions, regardless of the amount of fuel injected.

Degradation of the deNOx performance has been found in in-use heavy-duty vehicles with a urea-SCR system in Japan. The causes of the degradation were studied, and two major reasons are suggested here: HC poisoning and deactivation of pre-oxidation catalysts. Hydrocarbons that accumulated on the catalysts inhibited the catalysis. Although they were easily removed by a simple heat treatment, the treatment could only partially recover the original catalytic performance for the deNOx reaction. The unrecovered catalytic activity was found to result from the decrease in conversion of NO to NO2 on the pre-oxidation catalyst. The pre-oxidation catalyst was thus studied in detail by various techniques to reveal the causes of the degradation: Exhaust emission tests for in-use vehicles, effect of heat treatment on the urea-SCR systems, structural changes and chemical changes in active components during the deactivation were systematically investigated.

Cars are highly dependent on catalyst-based aftertreatment technology today due to tighter exhaust emission regulations. Since catalyst performance degradation over long-term operation is a major concern, onboard diagnostic (OBD) technology is becoming increasingly important. This paper presents new three-way catalyst diagnostic methods that can be applied under various driving conditions. Their effectiveness in meeting OBD requirements was evaluated when applied to CNG vehicles, which will be introduced in Europe. In the conventional catalyst diagnostic routine, large variation in the air-fuel ratio is generated when performing diagnosis, and catalyst degradation is determined by evaluating the signal response of an O2 sensor installed downstream of the catalyst. However, this method can only be used in conditions close to steady-state operation. In real-world driving, where a variety of operating conditions are possible, the rate of catalyst monitoring may decrease.