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Two-dimensional PIV was used to measure the cycle to cycle variability of large-scale flow-structures at TDC in a motored, two-valve, four-stroke engine. Over two hundred velocity distributions were measured for both a highly directed flow using a shrouded valve and a relatively undirected flow using a standard valve. Each cycle of the directed flow had the appearance of the single large swirl structure seen in the ensemble mean. Cyclic variability of the large-scale flow structure was manifest as variations in swirl ratio (rotational speed). Generally the variability was limited to scales smaller than 10 mm in size. For the undirected flow, none of cycles had the appearance of the ensemble mean. The flow appeared to be multimodal in that large-scale flow-structure patterns could be classified into three types based on flow-pattern recognition.

This study is an experimental and computational investigation of the influence of injection timing, fuel spray orientation, and in-cylinder air motion on the combustion, fuel economy, and engine-out emissions of a single-cylinder, 2-valve, spark-ignition direct-injection (SIDI) engine, operating under stratified-charged conditions. For the best compromise between fuel consumption, combustion stability, engine-out hydrocarbon emissions and smoke, the engine required relatively retarded injection timings (in comparison to other charge- or wall-controlled DI engines), high swirl levels, and a spray orientation that is directed towards the intake-valve side and targets the ridge wall of the piston.

In previous work, Reuss [1] studied the cycle-to-cycle variation in the large-scale velocity structures of high and low-swirl in-cylinder flows of an IC engine. The vector flow fields were obtained from PIV measurements in a two-valve, pancake-shaped, Transparent Combustion Chamber (TCC) engine. In this study, the Reynolds-decomposed turbulence properties such as kinetic energy, length scales, and dissipation rate were directly measured for the two cases. The results demonstrate that, at TDC compression, the low-swirl flow is dominated by turbulence at the largest scales, whereas the high-swirl flow has a considerably lower turbulence Reynolds number. The dissipation rate and length scale calculated from mixing-length theory greatly exceeded the dissipation computed from the 2-D velocity-gradients and integral-length scales computed from the autocorrelation, respectively.

Developing a complete understanding of the structure and behavior of the near-wall region (NWR) in reciprocating, internal combustion (IC) engines and of its interaction with the core flow is needed to support the implementation of advanced combustion and engine operation strategies, as well as predictive computational models. The NWR in IC engines is fundamentally different from the canonical steady-state turbulent boundary layers (BL), whose structure, similarity and dynamics have been thoroughly documented in the technical literature. Motivated by this need, this paper presents results from the analysis of two-component velocity data measured with particle image velocimetry near the head of a single-cylinder, optical engine. The interaction between the NWR and the core flow was quantified via statistical moments and two-point velocity correlations, determined at multiple distances from the wall and piston positions.