Optical Study of Flow and Combustion in an HCCI Engine with Negative Valve Overlap

Abstract

One of the most widely used methods to enable Homogeneous Charge Compression Ignition (HCCI) combustion is using negative valve overlapping to trap a sufficient quantity of hot residual gas. The characteristics of air motion with specially designed valve events having reduced valve lift and durations associated with HCCI engines and their effect on subsequent combustion are not yet fully understood. In addition, the ignition process and combustion development in such engines are very different from those in conventional spark-ignition or diesel compression ignition engines. Very little data has been reported concerning optical diagnostics of the flow and combustion in the engine using negative valve overlapping. This paper presents an experimental investigation into the in-cylinder flow characteristics and combustion development in an optical engine operating in HCCI combustion mode. PIV measurements have been taken under motored engine conditions to provide a quantitative flow characterisation of negative valve overlap in-cylinder flows. The ignition and combustion process was imaged using a high resolution charge coupled device (CCD) camera and the combustion imaging data was supplemented by simultaneously recorded in-cylinder pressure data which assisted the analysis of the images. It is found that the flow characteristics with negative valve overlapping are less stable and more valve event driven than typical spark ignition in-cylinder flows, while the combustion initiation locations are not uniformly distributed.

A Control-Oriented Two-Zone Charge Mixing Model for HCCI Engines With Experimental Validation Using an Optical Engine

“…Unfortunately, there are no available sensors other than pressure transducers that are capable of measuring incylinder properties because of high pressure and temperature in a cylinder. Due to such restriction, an optical engine has drawn attention for ICE research, since it allows direct optical access to the inside of a cylinder so that significant features like fuel spray injection and combustion flame propagation can be captured by images [15,16,22]. In this research, an IR camera was used to estimate the mean temperature of two zones during the intake stroke.…”

“…Thus instead of gas, soot which is one of combustion products is generally employed for an optical engine test to estimate the combustion temperature, because it has much higher emissivity than gas. There have been many efforts to estimate soot emissivity for optical engine research [15,16,22].…”

“…And GT-power simulation is carried out to further assist the model validation. Since an optical engine enables direct access inside a combustion chamber, it is broadly used in ICEs researches, particularly for diagnostic applications such as detection of fuel spray injection and combustion flame propagation [15,16]. In this research, mean temperature of two zones is estimated by radiation measurement with an IR camera.…”

Imaging studies of in-cylinder HCCI combustion

“…The widespread optical diagnostics techniques applicable to engine research field provide substantial, valuable and detailed insight into flow, auto-ignition or combustion activities patterns, and governing mechanisms by chemical species identification or eventual visualization of the aforementioned processes reflected by images [2,3]. The autoignition initiation and combustion development study using high-imaging speed imaging (CDD camera) technique in pure and spark assisted HCCI were reported by Aleiferis et al [4].…”