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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].

The effects of engine and after-treatment control conditions on emissions fluctuation were evaluated and the technical idea for improving the repeatability in tailpipe emission measurement from DISI vehicles was provided. To improve measurement repeatability, low emissions analyzers with dilution air refining system were employed for this research. In addition, a new device that enabled monitoring of signals from the Engine Control Unit (ECU) was developed. A novel approach using these devices was applied to DISI gasoline engine vehicles equipped with de-NOx catalyst to clarify emission characteristics in the Japanese 10.15 test cycle emission tests. Through the tests, it is found that NOx emissions most correlated with the temperature at the de-NOx catalyst. CO and HC reaching the de-NOx catalyst played an important role in the temperature increase of de-NOx catalyst by exothermic reactions.

Exhaust emissions from a vehicle under road driving condition is affected by the control state of ECU (Engine Control Unit). This control state highly depends on the driving force of the vehicle. The driving force is nearly equal to the driving resistance, which is the sum of the acceleration resistance, the air resistance, the rolling resistance and the gradient resistance. Although it is essential to take an accurate measurement of the road gradient, it is quite difficult to evaluate the gradient resistance in testing on-road driving. In this study, the measurement methods of the road gradient and the altitude with GPS, gyro sensor and height sensor are reported. The road gradient under the on-road driving condition is evaluated by the combination of measuring the pitch angle with the gyro sensor and measuring the vehicle gradient with the two height sensors. Verifying of this method, the altitude of the driving test route is also evaluated.

Exhaust emissions behavior from a vehicle under road driving condition is affected by a driving force of a vehicle. It is impossible to measure the driving force by an existing torque meter under this on-road driving condition. This study reports the development and verification of the wheel torque meter which is possible to measure driving force under the on-road driving condition and has enough strength and accuracy. The wheel torque meter developed in this study consists of a torque detector with a strain gauge type torque transducer, a telemeter receiver and a data logger. The strain gauge type torque transducer is equipped between hub and wheel at the drive axle tire, because of the narrow width of this transducer, and it is possible to be placed against vehicle without significant conversion of the vehicle. Because of these characters, this transducer is possible to be used for an on-road driving vehicle.