Nick J. Killingsworth

HCCI Engine Combustion-Timing Control: Optimizing Gains and Fuel Consumption Via Extremum Seeking

Homogenous-charge-compression-ignition (HCCI) engines have the benefit of high efficiency with low emissions of NOx and particulates. These benefits are due to the autoignition process of the dilute mixture of fuel and air during compression. However, because there is no direct-ignition trigger, control of ignition is inherently more difficult than in standard internal combustion engines. This difficulty necessitates that a feedback controller be used to keep the engine at a desired (efficient) setpoint in the face of disturbances. Because of the nonlinear autoignition process, the sensitivity of ignition changes with the operating point. Thus, gain scheduling is required to cover the entire operating range of the engine. Controller tuning can therefore be a time-intensive process. With the goal of reducing the time to tune the controller, we use extremum seeking (ES) to tune the parameters of various forms of combustion-timing controllers. In addition, in this paper, we demonstrate how ES can be used for the determination of an optimal combustion-timing setpoint on an experimental HCCI engine. The use of ES has the benefit of achieving both optimal setpoint (for maximizing the engine efficiency) and controller-parameter tuning tasks quickly.

A simple HCCI engine model for control

The homogenous charge compression ignition (HCCI) engine is an attractive technology because of its high efficiency and low emissions. However, HCCI lacks a direct combustion trigger making control of combustion timing challenging, especially during transients. To aid in HCCI engine control we present a simple model of the HCCI combustion process valid over a range of intake pressures, intake temperatures, equivalence ratios, and engine speeds. The model provides an estimate of the combustion timing on a cycle-by-cycle basis. An ignition threshold, which is a function of the in-cylinder motored temperature and pressure is used to predict start of combustion. This model allows the synthesis of nonlinear control laws, which can be utilized for control of an HCCI engine during transients.

Auto-tuning of PID controllers via extremum seeking

The proportional-integral-derivative (PID) controller is widely used in the process industry, but to various degrees of effectiveness because it is sometimes poorly tuned. The goal of this work is to present a method using extremum seeking (ES) to tune the PID parameters such that optimal performance is achieved. ES is a non-model based method which searches on-line for the parameters which minimize a cost function; in this case the cost function is representative of the controllers performance. Furthermore, this method has the advantage that it can be applied to plants in which there is no knowledge of the model. We demonstrate the ES tuning method on a cross section of plants typical of those found in industrial applications. The PID parameters are tuned based on the results of step response simulations to produce a response with minimal settling time and overshoot. Additionally, we have compared these results to those found using other tuning methods widely used in industry.

Extremum Seeking Tuning of an Experimental HCCI Engine Combustion Timing Controller

Homogenous charge compression ignition (HCCI) engines have the benefit of high efficiency with low emissions, at the price of not having a direct means to control the combustion timing. This fact makes combustion timing control of an HCCI engine more difficult than in spark ignition and diesel engines. While PID controllers have proved effective at isolated operating points, gain scheduling is needed to cover the entire range of operation. We use extremum seeking to tune the combustion timing controller of an experimental HCCI engine. Extremum seeking is found to be a useful tool for quick determination of optimal controller parameters. Such a tool allows for HCCI combustion timing controllers to be tuned over the range of operating points. I. Introduction

Development and Testing of a 6-Cylinder HCCI Engine for Distributed Generation

This paper describes the technical approach for converting a Caterpillar 3406 natural gas spark ignited engine into HCCI mode. The paper describes all stages of the process, starting with a preliminary analysis that determined that the engine can be operated by preheating the intake air with a heat exchanger that recovers energy from the exhaust gases. This heat exchanger plays a dual role, since it is also used for starting the engine. For start-up, the heat exchanger is preheated with a natural gas burner. The engine is therefore started in HCCI mode, avoiding the need to handle the potentially difficult transition from SI or diesel mode to HCCI. The fueling system was modified by replacing the natural gas carburetor with a liquid petroleum gas (LPG) carburetor. This modification sets an upper limit for the equivalence ratio at φ∼0.4, which is ideal for HCCI operation and guarantees that the engine will not fail due to knock. Equivalence ratio can be reduced below 0.4 for low load operation with an electronic control valve. Intake boosting has been a challenge, as commercially available turbochargers are not a good match for the engine, due to the low HCCI exhaust temperature. Commercial introduction of HCCI engines for stationary power will therefore require the development of turbochargers designed specifically for this mode of operation. Considering that no appropriate off-the-shelf turbocharger for HCCI engines exists at this time, we are investigating mechanical supercharging options, which will deliver the required boost pressure (3 bar absolute intake) at the expense of some reduction in the output power and efficiency. An appropriate turbocharger can later be installed for improved performance when it becomes available or when a custom turbocharger is developed. The engine is now running in HCCI mode and producing power in an essentially naturally aspirated mode. Current work focuses on developing an automatic controller for obtaining consistent combustion in the 6 cylinders. The engine will then be tested for 1000 hours to demonstrate durability. This paper presents intermediate progress towards development of an HCCI engine for stationary power generation and next steps towards achieving the project goals.Copyright

Development of Kinetic Mechanisms for Next-Generation Fuels and CFD Simulation of Advanced Combustion Engines

Predictive chemical kinetic models are needed to represent next-generation fuel components and their mixtures with conventional gasoline and diesel fuels. These kinetic models will allow the prediction of the effect of alternative fuel blends in CFD simulations of advanced spark-ignition and compression-ignition engines. Enabled by kinetic models, CFD simulations can be used to optimize fuel formulations for advanced combustion engines so that maximum engine efficiency, fossil fuel displacement goals, and low pollutant emission goals can be achieved.