Date of Award
2024
Document Type
Open Access Dissertation
Degree Name
Doctor of Philosophy in Mechanical Engineering-Engineering Mechanics (PhD)
Administrative Home Department
Department of Mechanical Engineering-Engineering Mechanics
Advisor 1
Jeremy Worm
Committee Member 1
Jeffrey Naber
Committee Member 2
Jeffrey Allen
Committee Member 3
Suneeta Sane
Abstract
Spark ignition engine knock is an issue that has persisted for over a century. Knock prevents the spark in an SI engine to be deployed at the most optimum time in the engine cycle, which leads to a decrease in the efficiency of the engine. A reduction in the efficiency directly translates to increased emissions and fuel costs. This research looks at experimental works to analyze the impact of three separate factors on knock in an effort to minimize it and improve engine efficiency.
The first factor is fuel chemistry – how Research Octane Number (RON) and Motor Octane Number (MON) of a fuel impact modern day turbocharged SI engines. The anti-knock behavior of an engine at a speed-load point can be determined by Octane Index (OI), which is defined as OI = RON – K*(RON-MON), where ‘K’ is a weighing factor that depends on the speed-load condition of the engine. As ‘K’ approaches 0, the anti-knock behavior of the engine can be described better by RON, and as ‘K’ approaches 1, it can be better described by MON. SI engines have undergone a lot of change in the past few decades, causing ‘K’ to venture past RON and have negative values. ‘K’ was defined to be independent of fuel chemistry, but previous studies had not calculated ‘K’ using the primary reference fuel (PRF) method. This research project used the PRF method to calculate fuel K-factor for Environmental Protection Agency (EPA) Certification Tier 2 and Tier 3 fuels. Correlations were developed to predict ‘K’ using macroscopic and microscopic factors.
The second factor is water injection – injecting water to lower in-cylinder temperatures and mitigate knock. Water injection has been used as a knock mitigation tool for a lot of years, but there hasn't been a proper quantification of the amount of increase in effective octane number water injection can provide. The experimental project conducted as a part of this dissertation used port water injection to quantify the effective increase in anti-knock index (AKI) of fuels. The same process was repeated on PRFs to determine the impact of water injection on increase in Octane Number (ON).
The third factor is heat transfer – there have been a plethora of studies conducted on how engine knock impacts heat transfer out of the engine, but no study on how heat transfer impacts knock. The study conducted as a part of this dissertation on a single cylinder research engine (SCRE) studied the relationship between heat transfer before the occurrence of knock with knock magnitude and frequency. As a part of this project, a non-intrusive method was developed to gauge the cleanliness of the heat flux probes. A speed-load condition was determined to maintain the cleanliness level of the probes without the buildup of carbon deposits.
The dissertation also attempts to find common themes between the three factors impacting knock and suggests future research paths to better understand ways to curb the issue of knock.
Recommended Citation
Gopujkar, Siddharth, "ANALYSIS OF FACTORS AFFECTING ENGINE KNOCK IN MODERN SPARK IGNITION GASOLINE ENGINES TO IMPROVE ENGINE EFFICIENCY", Open Access Dissertation, Michigan Technological University, 2024.