Experimental investigation for adopting hcci combustion in a diesel engine

Abstract

At present diesel engines are performing well and meeting existing emission norms. But to meet future emission norms alternative combustion concept may be useful. Homogeneous Charge Compression Ignition (HCCI) has proven to be capable of reducing both Oxides of Nitrogen (NOx) and Smoke emissions significantly. In HCCI engine, a homogeneous air fuel mixture is formed in the combustion chamber and the mixture is compression ignited. Due to the fact that the mixture is homogeneous, there is no smoke producing fuel-rich regions. The NOx emissions are also low because HCCI engine runs with lean homogeneous mixture and at low in-cylinder temperature. The objective of present work is for adopting HCCI combustion in a diesel engine by addressing the problems associated with HCCI engine like (i) rapid pressure rise due to instantaneous combustion (ii) difficulty to operate at higher loads due to knocking (iii) increase of HC and CO emissions (iv) decrease in brake thermal efficiency. At high loads, rate of pressure rise is rapid in the combustion chamber. Because of this, it is inevitable to sacrifice to run the engine at high loads with HCCI concept. Also CO and HC emissions for HCCI engine were reported to be increased, which requires a remedy. The another important problem is loss in brake thermal efficiency with HCCI combustion. Hence, there is a need to focus attention to overcome these problems in order to make HCCI engine practicable. Keeping these things in mind, experimental investigation is planned in the present research work to find remedies to the above problems. For this purpose, a computerized single cylinder, four stroke, water cooled, variable compression ratio, diesel engine is selected with specifications shown in Appendix-I. The performance, emission and combustion parameters of base engine diesel are recorded at standard operating conditions such as compression ratio 16.5, injection timing 230 bTDC and injection pressure 200 bar and these readings are taken as base data.