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research-article

Knock Intensity Distribution and a Stochastic Control Framework for Knock Control

[+] Author and Article Information
Mateos Kassa

Illinois Institute of Technology
mkassa@hawk.iit.edu

Carrie Hall

Illinois Institute of Technology
chall9@iit.edu

Michael Pamminger

Illinois Institute of Technology
mpamminger@hawk.iit.edu

Thomas Wallner

Argonne National Laboratory
twallner@anl.gov

1Corresponding author.

ASME doi:10.1115/1.4044437 History: Received December 01, 2017; Revised July 22, 2019

Abstract

One of the main factors limiting the efficiency of spark-ignited engines is the occurrence of engine knock. In high temperature and high pressure in-cylinder conditions, the fuel-air mixture auto-ignites creating pressure shock waves in the cylinder. Knock can significantly damage the engine and hinder its performance; as such, conservative knock control strategies are generally implemented that avoid such operating conditions at the cost of lower thermal efficiencies. Significant improvements in the performance of conventional knock controllers are possible if the properties of the knock process are better characterized and exploited in knock controller designs. One of the methods undertaken to better characterize knocking instances is to employ a probabilistic approach, in which the likelihood of knock is derived from the statistical distribution of knock intensity. In this paper, it is shown that knock intensity values at a fixed operating point for single fuel and dual fuel engines are accurately described using a mixed lognormal distribution. The fitting accuracy is compared against those for a randomly generated mixed-lognormally distributed data set, and shown to exceed a 95% accuracy threshold for almost all of the operating points tested. Additionally, this paper discusses a stochastic knock control approach that leverages the mixed lognormal distribution to adjust spark timing based on knock intensity measurements. This more informed knock control strategy would allow for improvements in engine performance and fuel efficiency by minimizing knock occurrences.

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