1. Introduction

Diesel engines have been widely popularized as a power source for vehicles owing to its reliable horsepower and excellent fuel economy. In Europe, especially, they occupy an enormous market share in public transportation and private uses. However, the pollution caused by diesel-engine exhausts has become more and more severe in the last decade, while the exhausts of gasoline-fueled engines operated near stoichiometric air/fuel ratio have been successfully cleaned up by three-way catalytic systems. In China, the emission of diesel particulate matter has become one of the primary sources of PM_2.5 pollution in cities. The emission from diesel engines is still a teaser, which bothering the scientific researchers and policymakers for years and it is affected by many factors such as the horsepower of vehicles, the composition of diesel, and combustion parameters.