Understanding the Dynamic Evolution of Cyclic Variability at the Operating Limits of HCCI Engines with Negative Valve Overlap

Abstract

An experimental study is performed for homogeneous charge compression ignition (HCCI) combustion focusing on late phasing conditions with high cyclic variability (CV) approaching misfire. High CV limits the feasible operating range and the objective is to understand and quantify the dominating effects of the CV in order to enable controls for widening the operating range of HCCI. A combustion analysis method is developed for explaining the dynamic coupling in sequences of combustion cycles where important variables are residual gas temperature, combustion efficiency, heat release during re-compression, and unburned fuel mass. The results show that the unburned fuel mass carries over to the re-compression and to the next cycle creating a coupling between cycles, in addition to the well known temperature coupling, that is essential for understanding and predicting the HCCI behavior at lean conditions with high CV.

Cyclic Variability and Dynamical Instabilities in Autoignition Engines With High Residuals

“…In order to satisfy the typical demands of speed and load, frequent transitions to the SI combustion mode would be required. Outside the stable operating range, HCCI combustion can exhibit significant oscillations at late phasing [2]- [4] and increasingly earlier combustion at high loads [5], even though all controllable inputs are held constant. Indeed, at certain operating conditions, HCCI combustion phasing can be: 1) oscillatory, where it alternates between early and late combustion phasing, or 2) unstable, where the combustion phasing occurs earlier for every cycle.…”

Effects of Direct Fuel Injection Strategies on Cycle-by-Cycle Variability in a Gasoline Homogeneous Charge Compression Ignition Engine: Sample Entropy Analysis

“…However, their experiments were performed for port injected engine. Correlations between consecutive engine cycles were also studied by Hellström et al [17]. They found that the subsequent cycles were coupled by feedback from incomplete combustion.…”

“…During the last decade a lot of effort was put into understanding the mechanisms of cyclic variability in HCCI engines [14][15][16][17][18][19][20][21]. Koopmans et al [14] presented the mechanism of cyclic variability of combustion timing in an engine with direct NVO injection.…”

“…They have also demonstrated peak pressure patterns at engine operation close to the misfire limit. Recently, understanding of the cyclic variability nature in HCCI engines became a keystone for the development of control algorithms for stabilization of cyclic dispersion [17,18,21,[23][24][25].…”

Control of a dual-loop exhaust gas recirculation system for a turbocharged Diesel engine

“…However, they can only be achieved in a very narrow range of operating conditions and close to the combustion stability boundaries (Chiang and Stefanopoulou, 2006;Hellström et al, 2012). It turns out that the in-cylinder conditions, such as the burned gas fraction, temperature and pressure are of critical importance in controlling advanced combustion modes (Ravi et al, 2010).…”