Understanding fuel anti-knock performances in modern SI engines using fundamental HCCI experiments

Journal Article · Wed Aug 19 00:00:00 EDT 2015 · Combustion and Flame

DOI:https://doi.org/10.1016/j.combustflame.2015.07.040· OSTI ID:1343270

Yang, Yi ^[1]; Dec, John E. ^[2]; Sjoberg, Magnus ^[2]; Ji, Chunsheng ^[2]

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1. Univ. of Melbourne (Australia); Sandia National Lab. (SNL-CA), Livermore, CA (United States)
2. Sandia National Lab. (SNL-CA), Livermore, CA (United States)

Modern spark-ignition (SI) engine technologies have considerably changed in-cylinder conditions under which fuel autoignition and engine knock take place. In this paper, fundamental HCCI engine experiments are proposed as a means for characterizing the impact of these technologies on the knock propensity of different fuels. In particular, the impacts of turbocharging, direct injection (DI), and downspeeding on operation with ethanol and gasoline are investigated to demonstrate this approach. Results reported earlier for ethanol and gasoline on HCCI combustion are revisited with the new perspective of how their autoignition characteristics fit into the anti-knock requirement in modern SI engines. For example, the weak sensitivity to pressure boost demonstrated by ethanol in HCCI autoignition can be used to explain the strong knock resistance of ethanol fuels for turbocharged SI engines. Further, ethanol's high sensitivity to charge temperature makes charge cooling, which can be produced by fuel vaporization via direct injection or by piston expansion via spark-timing retard, very effective for inhibiting knock. On the other hand, gasoline autoignition shows a higher sensitivity to pressure, so only very low pressure boost can be applied before knock occurs. Gasoline also demonstrates low temperature sensitivity, so it is unable to make as effective use of the charge cooling produced by fuel vaporization or spark retard. These arguments comprehensively explain literature results on ethanol's substantially better anti-knock performance over gasoline in modern turbocharged DISI engines. Fundamental HCCI experiments such as these can thus be used as a diagnostic and predictive tool for knock-limited SI engine performance for various fuels. As a result, examples are presented where HCCI experiments are used to identify biofuel compounds with good potential for modern SI-engine applications.

• Research Organization: Sandia National Lab. (SNL-CA), Livermore, CA (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC04-94AL85000
• OSTI ID: 1343270
• Alternate ID(s): OSTI ID: 1247768
• Report Number(s): SAND-2017-0915J; PII: S0010218015002485
• Journal Information: Combustion and Flame, Vol. 162, Issue 10; ISSN 0010-2180
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

33 ADVANCED PROPULSION SYSTEMS
knock propensity
HCCI
turbocharging
DISI
ethanol