Browsing by Subject "Ignition Delay"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Design, Control, and Characterization of a Controlled Trajectory Rapid Compression and Expansion Machine (CT-RCEM)
    (2019-08) Tripathi, Abhinav
    This thesis presents the design, control and characterization of a novel experimental facility for fundamental and applied combustion investigations – a controlled trajectory rapid compression and expansion machine (CT-RCEM). Rapid compression machine (RCM) has been a popular experimental facility used for the investigation of combustion characteristics of fuels in low to intermediate temperature ranges. The CT-RCEM, developed in this research, addresses a key limitation of the conventional RCM, i.e. an open-loop and calibration-based actuation philosophy. The CT-RCEM uses an electrohydraulic actuator driven by a precise motion controller to drive the piston in the combustion chamber. Any changes in the operating parameters can thus be made by electronically changing the piston trajectory sent to the controller, unlike the conventional RCM which requires hardware intervention. This allows the CT-RCEM to provide ultimate flexibility in the choice of operating parameters, a wider operating range with higher resolution, lower turnaround time, and exceptional run-to-run repeatability. The key novelty of CT-RCEM, however, lies in the new paradigm of experimental investigation enabled by the ability to tailor the thermodynamic path inside the combustion chamber by suitable choice of piston trajectory. Specific examples include, the ability to investigate the effect of changing the thermodynamic path of compression on ignition delay, the ability to quench the chemical kinetics in the combustion chamber by extremely rapid expansion, and, the ability to produce isobaric conditions inside combustion chamber by slow creeping of the piston at a rate which offsets the rate of wall heat loss. In this research, first, a control oriented dynamic model of the CT-RCEM is developed. The model serves three purposes for the development of the CT-RCEM – (i) to understand the impact of various design parameters of the CT-RCEM on its performance and tuning them to obtain a suitable mechanical design; (ii) to design a model based high bandwidth controller that can provide precise tracking performance for the piston motion (iii) to guide the design of the various subsystems of the CT-RCEM. Next, a model based, iterative learning control (ILC) scheme is implemented for the control of the actuation system of the CT-RCEM. Since the choice of the initial control signal for the first iteration has a significant impact on the number of iterations required for ILC convergence, the initial signal for the ILC is generated through simulation, from the dynamic model of the CT-RCEM, which uses a repetitive controller. This is followed by the characterization of the CT-RCEM which essentially involves demonstrating that the facility can provide the desired functionality – fast compression and repeatable pressure history – over the designed operating range for both non-reactive and reactive mixtures. Also, the new capabilities of CT-RCEM enabled by the ability to tailor the thermodynamic path are demonstrated. Next, the utility of the CT-RCEM is demonstrated for applied engine research where a single combustion event of an engine can be recreated with well controlled initial and boundary conditions. It is demonstrated that the CT-RCEM can be used to perform a benchmarking study of the combustion characteristics of a realistic free piston engine operation and its effect on the piston trajectory by presenting a case study. Finally, a multi-zone thermo-kinetic model is developed for computationally efficient analysis of the experimental data obtained from the CT-RCEM. A reaction path analysis performed using this model is used to explain a highly counter-intuitive experimental observation made using the CT-RCEM – a faster compression does not necessarily lead to smaller pre-ignition reaction progress during compression and (consequently) a longer ignition delay. It is shown that the degree of pre-ignition reaction progress and consequently the radical pool at the end of compression can be quite sensitive to the thermodynamic path of compression, not just the end of compression thermodynamic state.