Date of Award
12-2025
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Automotive Engineering
Committee Chair/Advisor
Benjamin Lawler
Committee Member
Brian Gainey
Committee Member
Harsh Sapra
Abstract
Stochastic end-gas autoignition in SI engines, commonly called ‘knock’, limits attainable engine efficiencies. Multiple pathways to extend SI engine operation into knock-limited regions have been studied, including direct water injection (DWI). This study employs single-cylinder engine experiments and modeling to investigate the knock resistance offered by compression stroke water injections, which have shown to thermally stratify the cylinder in HCCI. In SI, thermally stratifying injections are expected to forcibly widen the cylinder temperature distribution by preferentially cooling the cylinder periphery. The end-gas is in the cylinder periphery; therefore, a cooler end-gas would result in longer ignition delays, thus providing knock resistance.
The difference between intake air temperature required to match knock-limited CA50 conditions, and a baseline intake temperature at the load of 8 bar IMEPg was used to quantify the ‘effective charge cooling’ for the injection timings studied. Early compression stroke injections (-180 to -120 aTDC) provided higher effective charge cooling compared to later compression stroke and intake stroke injections. A compression stroke SOI sweep was performed at a non-knocking load of 6 bar IMEPg while holding the spark timing, intake temperature, and water mass constant to study the effect of SOI on the combustion process. Although CA50 advanced while delaying the SOI (-180 to -80 aTDC), post-CA50 burn durations stayed nearly constant, a behavior consistent with the presence of thermal stratification. Thus, it was concluded that injection timings which heterogeneously cool the cylinder extract higher knock resistance compared to bulk cooling.
Recommended Citation
Datar, Aditya, "Study on the Knock Resistance Offered by Thermally Stratifying Water Injections in a Single Cylinder Spark Ignition Engine" (2025). All Theses. 4647.
https://open.clemson.edu/all_theses/4647