Experimental Investigation of Impinging Diesel Sprays for HCCI Combustion

Abstract: Engine research and development is to a large extent driven by the quest of lowering exhaust emissions and fuel consumption. The combination of low emissions and low fuel consumption is not the simultaneous characteristic of the world’s primary engine concepts, the diesel and the spark-ignited (SI) engine. However, such a concept do exist, it is commonly called Homogeneous Charge Compression Ignition (HCCI).The HCCI combustion concept is when a premixed air and fuel mixture is ignited by the heat of compression. The operation is unthrottled, like the diesel engine, which is advantageous for its efficiency. The premixed air / fuel mixture preclude soot formation, like the SI engine. An exclusive feature of HCCI combustion is extremely low NOX production due to low-temperature combustion.The mixture preparation of the typical gasoline HCCI engine is similar to the SI engine, via port-injection, which results in a well homogenized mixture. Port injection of diesel fuel is however very difficult since the environment is too cold for the fuel to vaporise. A better alternative is therefore direct-injection. However, injection must occur in a way where a homogeneous mixture is formed, while contact of the liquid fuel with cold walls is avoided.There are many approaches to direct-injected mixture formation. This thesis focuses on exploring the concept of impinging sprays; its characteristics and its impact on combustion and emissions. The work comprises unique information regarding impinging sprays, as well as results regarding engine performance. It is concluded that impinging sprays are well suited for early direct-injection.