Fossil fuels such as oil, gas, and coal have driven the world's economies since the industrial revolution and have released carbon emissions in the process. About 26 billion tons of carbon dioxide are produced every year and this is still increasing. The 1997 Kyoto agreement is the world's only attempt to regulate carbon emissions. Diesel engines have been widely used as the major propulsion power sources because of their simple, robust construction coupled with high thermal efficiency and specific power output with high fuel economy. However, diesel engines are the major contributors of various types of air pollutants such as carbon monoxide (CO), oxides of nitrogen (NO x), particulate matter (PM), and other harmful compounds. The reduction in engine emissions is a major research objective in the engine development because of increasing concern for the environment pollution and more stringent government regulation on exhaust emissions. It is difficult to reduce PM and NO x simultaneously owing to the trade-off between PM and NO x [1]