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Time-Resolved In-Cylinder Heat Transfer and its Implications on Knock in Spark Ignition Engines

Frederick, John David
http://rave.ohiolink.edu/etdc/view?acc_num=osu1437648508

Abstract Details

2015, Master of Science, Ohio State University, Mechanical Engineering.
Spark Ignition (SI) engines power 96.6% of light duty vehicles produced in North America in 2013, yet the ability to increase their efficiency through strategies such as boosting or increasing the compression ratio is limited by knock. Knock, or the autoignition of the fuel and air mixture ahead of the flame front, is dictated by chemical kinetics and the rates of the reactions leading to autoignition are determined by the Boltzmann factor, which is exponentially dependent on the local gas temperature. The gas temperature is a function of both the heat release from combustion and the in-cylinder heat transfer. Therefore, to predict knock and operate SI engines as efficiently as possible, it is necessary to accurately model the in-cylinder heat transfer process. Hence, the objective of the present study is to improve the understanding of in-cylinder heat transfer of SI engines. Time-resolved in-cylinder heat transfer was measured in cylinder #4 of a Chrysler 2.0L I4 engine using Vatell Heat Flux Microsensors (HFMs) along with pressure measurements within the combustion chamber and in the intake runner and plenum as well as the exhaust runner. Firing engine experiments were first performed with a single heat flux sensor at 1600 and 2400 RPM wide open throttle (WOT). Carbon deposits built up on the HFM surface, necessitating the development of a sensor cleaning procedure using acetone as a solvent. An approximate pressure limit of 50 bar for the HFM was also determined with this cylinder head. Motored engine experiments were then performed with a multi-sensor cylinder head with two HFMs at 1200, 1600, 2000, 2400, and 3000 RPM WOT and the peak heat flux was observed to increase with increasing engine speed. Despite negligible variation of the in-cylinder pressure from cycle-to-cycle, cyclic variation of heat flux was significant at both measurement locations. Firing experiments with the multi-sensor cylinder head were completed at 1200, 1600, and 2000 RPM WOT. Significant spatial differences in heat flux were observed between the two measurement locations for firing operation. Peak heat flux measured between the intake and exhaust valves (HFM3) was 49% higher on average than at the intake bridge (HFM1) while also reaching peak magnitude earlier. Average flame propagation speeds in the direction of HFM3 were on average 46% higher than towards HFM1 as well. Similar to the motored experiments, high cyclic variability of heat flux was observed for all firing experiments. Even with considerable cycle-to-cycle variation, average in-cylinder pressure and heat flux measurements were found to be quite repeatable. Detailed 3D CFD simulations of cylinder #4 for motored and firing operation were performed at 1600 RPM WOT using CONVERGE CFD software. Predicted pressure and heat flux for motored operation matched the experimental results well. For the firing engine, combustion was modeled using a kinetics mechanism for a primary reference fuel blend (PRF 91). Both the predicted cylinder pressure and heat flux showed good agreement with the average measurements. The CFD-predicted heat transfer for the entire combustion chamber was implemented in the engine simulation tool GT-Power along with a kinetics-based knock model. Noteworthy differences were observed between GT-Power simulations using the CFD-predicted heat transfer and those using the conventional Woschni heat transfer correlation. The CFD-predicted heat transfer simulations showed substantial differences in the phasing of first stage ignition as well as cylinder pressure. Both the phasing of first stage ignition and cylinder pressure have significant implications on the potential onset and severity of knock, demonstrating the importance of improved heat transfer modeling in accurately simulating knock and engine performance.
Ahmet Selamet, PhD (Advisor)
Junmin Wang, PhD (Committee Member)
Ronald Reese, II (Committee Member)
199 p.
Mechanical Engineering
Knock; Heat Transfer; Spark Ignition Engines; Combustion

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Citations

  • Frederick, J. D. (2015). Time-Resolved In-Cylinder Heat Transfer and its Implications on Knock in Spark Ignition Engines [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1437648508

    APA Style (7th edition)

  • Frederick, John. Time-Resolved In-Cylinder Heat Transfer and its Implications on Knock in Spark Ignition Engines. 2015. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1437648508.

    MLA Style (8th edition)

  • Frederick, John. "Time-Resolved In-Cylinder Heat Transfer and its Implications on Knock in Spark Ignition Engines." Master's thesis, Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1437648508

    Chicago Manual of Style (17th edition)

osu1437648508
151
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This open access ETD is published by The Ohio State University and OhioLINK.