Shyam Jade

Reducing Cyclic Variability While Regulating Combustion Phasing in a Four-Cylinder HCCI Engine

The cyclic variability (CV) at late phasing conditions in autoignition engines with high residuals limits the operating range of such advanced combustion strategies. A model has been recently proposed by the authors that captures the experimental observations of CV in lean autoignition combustion in a single-cylinder engine. The model is here tuned to multicylinder engine data and is used to design controllers that reduce the CV. The dynamics are only stable for certain amounts of residual gas. At late phasing, with low amounts of residual gas, a cascade of period-doubling bifurcations occur leading to seemingly chaotic behavior. The deterministic dynamics are also mixed with significant levels of noise in the residual gas fraction. The approach to reduce CV is to control the fuel injection timing, which is an effective way of influencing the combustion phasing in the individual cylinders, with feedback from the combustion phasing. A PI controller and a reduced-order linear quadratic Gaussian (LQG) controller are designed and evaluated in experiments. Integral action is utilized for maintaining the average combustion phasing between open loop and closed loop, which is shown to be essential for a proper evaluation because of the high sensitivity of CV on the combustion phasing close to unstable operation. A quantitative analysis of the experimental results show that CV is notably reduced for various levels of residual gas fraction at one speed and load. The standard deviation of the combustion phasing is reduced by 17% on average over the open-loop behavior, which results in a 15% smaller coefficient of variation of the indicated work.

Reference Governor for Load Control in a Multicylinder Recompression HCCI Engine

This paper presents a model-based control strategy designed to regulate combustion phasing during load transitions in a recompression homogeneous charge compression ignition (HCCI) engine. A low-order discrete-time control-oriented model for recompression HCCI combustion is developed that represents the strong thermal and composition coupling between engine cycles. A baseline two-input single-output controller is designed to regulate combustion phasing, using the amount of negative valve overlap and the fuel injection timing as actuators. This controller is augmented by a reference or fuel governor, which modifies transient fuel mass commands during large load transitions, when future actuator constraint violations are predicted. This approach is shown in experiments to improve combustion phasing and load responses, preventing engine misfires in some cases. The fuel governor enables larger load transitions than were possible with the baseline controller alone. The governor acts only when future actuator constraint violations are predicted. The complexity and computational overhead of the governor are reduced by developing a linearized fuel governor. Satisfactory performance is demonstrated experimentally for a range of engine speeds.

Fuel governor augmented control of recompression HCCI combustion during large load transients

A control strategy designed to track desired combustion phasing for a homogeneous charge compression ignition (HCCI) engine during large load transitions is presented in this work. Three inputs are controlled, namely valve timings, fuel injection amount and fuel injection timing. The valve and fuel injection timings are manipulated to track combustion phasing using a mid-ranging control strategy. A fuel governor is then added on to the compensated system to modify the fuel injection amount by enforcing pointwise-in-time actuator constraints. The fuel governor is shown to improve the transient response of combustion phasing and load during large load transitions, when the possibility of future constraint violations exists. The use of the fuel governor during large load reductions can prevent engine misfire. Moreover, the fuel governor strategy simplifies the overall controller design by decoupling the phasing controller from the constraint enforcing mechanism. System complexity is reduced by approximating the nonlinear fuel governor as a set of linear algebraic expressions. This is solved with very little computational overhead and without incurring a significant loss in performance, as presented in simulations.

Controlled Load and Speed Transitions in a Multicylinder Recompression HCCI Engine

A model-based control strategy to track combustion phasing during load and speed transitions in the homogeneous charge compression ignition (HCCI) operating region of a multimode combustion engine is presented in this paper. HCCI transitions can traverse regions of high cyclic variability (CV), even if the steady state transition end points are stable with low CV. A control-oriented HCCI model for both the stable, low CV region and the oscillatory, high CV, late phasing region is used to design a controller that uses valve and fuel injection timings to track combustion phasing. Novel aspects of the controller include nonlinear model-inversion-based feedforward and gain scheduled feedback based on unburned fuel that reduces transient CV. Transitions tested on a multicylinder HCCI engine include load transitions at fixed engine speeds, simultaneous load, and speed transitions, and select FTP75 drive-cycle transitions with high load slew rates. Good combustion phasing tracking performance is demonstrated, and misfires are prevented.

Enabling large load transitions on multicylinder recompression HCCI engines using fuel governors

The fuel governor control design methodology presented in [1] is extended and experimentally validated on a multicylinder recompression homogeneous charge compression ignition (HCCI) engine. This strategy regulates desired combustion phasing during load transitions across the HCCI load range. A baseline controller tracks combustion phasing by manipulating valve and fuel injection timings. A reference governor is then added on to the compensated system to modify the fuel injection amount by enforcing actuator constraints. Experimental results show improved transient responses of combustion phasing and load during load transitions, when the possibility of constraint violations exists. The nonlinear fuel governor predicts future model trajectories in real-time, and enables larger load transitions than were possible with the baseline controller alone. The complexity and computational overhead of this strategy are reduced by developing a linearized fuel governor, which is shown to work well in the entire HCCI load range and for small variations in engine speed.

On the Influence of Composition on the Thermally-Dominant Recompression HCCI Combustion Dynamics

A zero dimensional, mean-value, control-oriented model for recompression homogeneous charge compression ignition (HCCI) combustion with two discrete states representing temperature and composition dynamics is presented. This model captures steady state magnitudes and trends in combustion phasing, residual gas fraction, and mass flows caused by sweeps in valve timings, fueling rate, and fuel injection timing. It is shown that the coupling of the composition state with the mainly thermally-driven combustion dynamics causes competing slow and fast dynamics that shape the transient response of the phasing. A decoupled version of the model, where composition does not affect combustion phasing, is also developed in an effort to further simplify the model. This version matches the steady state fidelity of the coupled model, but has a qualitatively different dynamical behavior. Both models exhibit complex behaviors such as limit cycles at extremely late phasing. Both realizations are valid contenders as low order steady state representations of HCCI behavior. High-fidelity transient data will be necessary to further clarify the necessity of including composition effects on combustion phasing.

Controlling combustion phasing variability with fuel injection timing in a multicylinder HCCI engine

Reduction of combustion phasing cyclic variability (CV) in homogeneous charge compression ignition (HCCI) engines operating lean with late autoignition is experimentally demonstrated. A three-state discrete time model developed in [1] is used for controlling the fuel injection timing and is applied to a multicylinder engine. A key objective of this work is to reduce cyclic variability without advancing the mean combustion phasing. Specifically, if late combustion phasing can be made less variable without advancing the operating point then areas where high CV is typically encountered could be made less variable. Examples include load transition down, when the residual temperature drops more rapidly than can be manipulated by the valve timing, or during mode transitions. Experimental results are presented to gauge the effectiveness of two control schemes, namely proportional and state feedback which have been tuned using the three-state model. Each of these controllers have been augmented with an integrator to maintain the late combustion phasing requirement. This is also done to draw a fair comparison of the controllers ability to reduce CV. The controllers are tested at various levels of CV and it is found that simple control can reduce the standard deviation of combustion phasing an average of 17% over open loop behavior. In addition, because of the simplicity of the control, this offers a viable solution for commercial applications.

Adaptive Control of a Recompression Four-Cylinder HCCI Engine

An adaptive controller is presented for the control of combustion phasing in a multicylinder homogeneous charge compression ignition engine. Adaptive parameter estimation is used to modify a model-based feedforward controller for each cylinders start of injection (SOI) timing in an effort to mitigate model errors and increase the feedforward control accuracy. In-cylinder pressure measurements are used to calculate combustion phasing, which is compared with the prediction of an online nonlinear engine model to drive the parameter estimation that adapts the feedforward controller. It is demonstrated through experiments that the adaptive parameter can reduce the parameterization effort by allowing the model to adapt and match the response of each cylinder. It is also shown that the adaptive feedforward control is more accurate in the sense that load transitions can be achieved with less correction from the feedback controller. Overall, an average reduction of 41% in the absolute value of the SOI feedback component at steady state is achieved.

Real-time internal residual mass estimation for combustion with high cyclic variability

In this work, a physics-based method of estimating the residual mass in a recompression homogeneous charge compression ignition engine is developed and analyzed for real-time implementation. The estimation routine is achieved through in-cylinder pressure and exhaust temperature measurements coupled with energy and mass conservation laws applied during the exhaust period. Experimental results on a multicylinder gasoline homogeneous charge compression ignition engine and dynamic analysis demonstrate the estimation routine’s ability to perform across a wide range of operating conditions as well as on a cycle-by-cycle basis for highly variable combustion phasing data.

Online Adaptive Residual Mass Estimation in a Multicylinder Recompression HCCI Engine

This work presents two advances to the estimation of homogeneous charge compression ignition (HCCI) dynamics. Combustion phasing prediction in control-oriented models has been achieved by modeling the in-cylinder temperature and composition dynamics, which are dictated by the large mass of residuals trapped between cycles. As such, an accurate prediction of the residual gas fraction as a function of the variable valve timing is desired. Energy and mass conservation laws applied during the exhaust valve opening period are complemented with online in-cylinder pressure measurements to predict the trapped residual mass in real time. In addition, an adaptive parameter estimation scheme uses measured combustion phasing to adjust the residual mass prediction. Experimental results on a multicylinder gasoline HCCI engine demonstrate the closed loop residual estimation’s ability to compensate for modeling errors, cylinder to cylinder variations, and engine wear. Additionally it is shown that using the adaptive parameter estimation reduces the model parameterization effort for a multicylinder engine.Copyright