Physics-Based Modeling and Control of Residual-Affected HCCI Engines

Abstract

Homogeneous charge compression ignition (HCCI) is a novel combustion strategy for IC engines that exhibits dramatic decreases in fuel consumption and exhaust emissions. Originally conceived in 1979, the HCCI methodology has been revisited several times by industry but has yet to be implemented because the process is difficult to control. To help address these control challenges, the authors here outline the first generalizable, validated, and experimentally implemented physics-based control methodology for residual-affected HCCI engines. Specifically, the paper describes the formulation and validation of a two-input, two-state control-oriented system model of the residual-affected HCCI process occurring in a single engine cylinder. The combustion timing and peak pressure are the model states, while the inducted gas composition and effective compression ratio are the model inputs. The resulting model accurately captures the system dynamics and allows the simultaneous, coordinated control of both in-cylinder pressure and combustion timing. To demonstrate this, an H2 optimal controller is synthesized from a linearized version of the model and used to dictate step changes in both combustion timing and peak pressure within about four to five engine cycles on an experimental test bed. The application of control also results in reductions in the standard deviation for both combustion timing and peak pressure. The approach therefore provides accurate mean tracking, as well as a reduction in cyclic dispersion. Another benefit of the simultaneous coordination of both control inputs is a reduction in the control effort required to elicit the desired response. Instead of using a peak pressure controller that must compensate for the effects of a combustion timing controller, and vice versa, the coordinated approach optimizes the use of both control inputs to regulate both outputs.

Stability analysis of residual-affected HCCI using convex optimization

“…The dynamic coupling between VVA-controllable inputs (inducted gas composition and effective compression ratio) and measurable outputs of the residual-affected HCCI process (combustion timing and peak pressure) is captured with a 2-input 2-output control model (Shaver et al, 2008). The framework for developing the control model is to partition the engine cycle into five stages, as shown in Fig.…”

“…A simplified 2-state control model (constructed as a means to directly synthesize control strategies (Shaver, Roelle, & Gerdes, 2008) also shows this self-stabilizing behavior. Utilizing a physics-based approach, the control model, like the 10-state model, is capable of capturing the self-stabilizing behavior because it explicitly includes the effect that residual modulation has on the pre-compression and post-combustion temperatures, as well as their role in determining the timing of the combustion event via the chemical kinetics and cycle-to-cycle coupling through the exhaust gas temperature.…”

The use of different types of piston in an HCCI engine: A review

“…As noted above, there are three common types of piston designs used in HCCI gasoline-fuelled engines; flat, bowl, and dome. The choice of design depends on the desires of the manufacturer [44]. Therefore, there is a need to understand in-cylinder fluid dynamics, since it has been noted to be unsteady, three-dimensional, and turbulent.…”

“…Because of their purpose of reducing the compression ratio, these pistons are perfect for super-charged and turbo-charged engines [42,43]. The most common pistons in HCCI engines are bowl types, two-stroke pistons, dome-shaped pistons, and specialised pistons, each of which offers distinct advantages and disadvantages [44]. The advantage of bowl type pistons is that they can be used in a supercharged engine to avoid spark knock with the set conditions; a disadvantage of these is that, due to the hotter running piston, there is an increase in production of harmful gases like nitrogen oxides.…”

Constrained Nonlinear Predictive Control of Gasoline Low-Temperature Combustion

“…Decoupled control of the peak pressure and the combustion timing was proposed [4], as well as a coordinated peak pressure and combustion timing controller based on the linearization of a nonlinear physical model about an operating point which is implemented in an H 2 control strategy [5]. Gain scheduled linear MPC control of IMEP and CA50 in steps between stationary operating points with constraints on dpmax was realized using Wiener-type models for compensating for the nonlinear characteristics [6,7].…”