Diesel engines are participating a vital responsibility in the field of automobile, agriculture, construction and power generation. In present world, much research is going on in the field of renewable energy to replace conventional sources of energy. But it is not very easy to replace diesel engines with other engines when the power and reliability are the factors that matter. The emissions from diesel engines are very harmful for the environment and for human health. The major emissions are smoke and NOx which need to be controlled in an effective manner. This book covers the fundamental concept of enhancing performance and reducing the emissions of CI engine using bio-additives and different compression ratios.