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Utilization of biofuels to vehicles is attracting attention globally from viewpoints of preventing global warming, effectively utilizing the resources, and achieving the local invigoration. Representative examples are bioethanol and biodiesel. This study highlights biodiesel and hydrotreated vegetable oil (HVO) in view of reducing greenhouse gas emission from heavy-duty diesel vehicles. Biodiesel is FAME obtained through ester exchange reaction by adding methanol to oil, such as rapeseed oil, soybean oil, palm oil, etc. As already reported, FAME has fuel properties different from conventional diesel fuel, resulting in about 10% increase in NOx emission [1],[2],[3]. Suppression of such increase in the NOx emission during operating with biodiesel requires adjustment of the combustion control technology, such as fuel injection control and EGR, to the use of biodiesel.

The Eco-Driving technique which includes measures such as preventing sudden acceleration and shifting-up at lower engine speed is attractive because it has an immediate effect on reduction of CO2 emissions from vehicles with minimal effort. In order to determine the main factors for reducing CO2 emissions by Eco-Driving, tests on urban roads were conducted with a light duty diesel freight vehicle operated by five test drivers under two driving scenarios: one with typical operations and one with Eco-Driving operations. As a result, under conditions of a mean vehicle speed of about 15km/h, the amount of CO2 emissions emitted during Eco-Driving operations by the test drivers were less than those of typical operations by 15% or more. It was determined that while under Eco-Driving operations, CO2 emissions in acceleration modes were greatly reduced. Other modes like cruising, deceleration, and idling produced less CO2 reductions.

Hybrid trucks have now started to penetrate the Japanese market. To investigate their advantages for fuel economy and exhaust emissions, a real time on-board measurement system for fuel economy and NOx emissions was mounted in a medium duty hybrid truck with a capacitor system. Running tests were carried out with various payloads on roads. The results demonstrated the advantages of the hybrid truck in real traffic conditions. Fuel economy was improved on urban and suburban roads, as compared to a base diesel vehicle. The hybrid truck showed less NOx emissions during acceleration at starting, whereas, acceleration of diesel vehicles may cause intensive localized NOx pollution of roadsides, in places like intersections.

Hybrid trucks are disseminated on the market in Japan. To bring out advantages of fuel economy and low emission, on-board measuring system for fuel consumption and NOx emissions was mounted in a light duty truck with a parallel hybrid system. Tests were carried out with various payloads on roads. As the results, advantages of the tested hybrid truck were shown from the actual data regarding the fuel economy and NOx emissions, considering regeneration energy by the hybrid system. Improvement of the fuel economy and NOx emissions was clearly observed in the running condition such as urban and suburban roads. From the analysis of regeneration energy during vehicle deceleration, it turned out that a longer slowdown time and a higher speed at which deceleration begins result in larger amount of energy regeneration, which means the improvement of fuel economy. For the improvement of roadside pollutions, the reduction of NOx emissions in running using the second gear position is desired.