Modes of reaction front propagation from hot spots

Paczko

et al. 2016

Combustion and Flame

111

expresses the influences of hot spot temperature gradient and fuel characteristics, and a unique value of it might serve as a boundary between auto-ignitive and deflagrative regimes. Other combustion regimes can also be identified, including a mixed regime of both auto-ignitive and "normal" 2 deflagrative burning. The paper explores the performances of a number of different engines in the regimes of controlled auto-ignition, normal combustion, combustion with mild knock and, ultimately, super-knock. The possible origins of hot spots are discussed and it is shown that the dissipation of turbulent energy alone is unlikely to lead directly to sufficiently energetic hot pots. The knocking characterisation of fuels also is discussed.

Section: Excitation Time and The Detonation Peninsulamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Engine hot spots: Modes of auto-ignition and reaction propagation

Bates

Paczko

et al. 2016

Combustion and Flame

111

“…In the range of interest, t i is usually measured in milliseconds, and t e in microseconds. The rapidity of the unloading into the acoustic wave is quantified approximately by the number of excitation times that can be contained within r o /a, and is given by Gu et al [15] computed for a range of different conditions. As suggested above, development of a detonation depended not only on the value of x but also on that of 3.…”

Section: Autoignition Velocitiesmentioning

confidence: 99%

Autoignitions and detonations in engines and ducts

Phil. Trans. R. Soc. A.

2012

The origins of autoignition at hot spots are analysed and the pressure pulses that arise from them are related to knock in gasoline engines and to developing detonations in ducts. In controlled autoignition engines, autoignition is benign with little knock. There are several modes of autoignition and the existence of an operational peninsula, within which detonations can develop at a hot spot, helps to explain the performance of various engines. Earlier studies by Urtiew and Oppenheim of the development of autoignitions and detonations ahead of a deflagration in ducts are interpreted further, using a simple one-dimensional theory of the generation of shock waves ahead of a turbulent flame. The theory is able to indicate entry into the domain of autoignition in an 'explosion in the explosion'. Importantly, it shows the influence of the turbulent burning velocity, and particularly its maximum attainable value, upon autoignition. This value is governed by localized flame extinctions for both turbulent and laminar flames. The theory cannot show any details of the transition to a detonation, but regimes of eventually stable or unstable detonations can be identified on the operational peninsula. Both regimes exhibit transverse waves, triple points and a cellular structure. In the case of unstable detonations, transverse waves are essential to the continuing propagation. For hazard assessment, more needs to be known about the survival, or otherwise, of detonations that emerge from a duct into the same mixture at atmospheric pressure.

“…Another approach has been to employ ignition delay and excitation times, embodied in the developing detonation peninsula regime, plotted on a diagram of   / coordinates [4]. Here  is the acoustic speed, a, normalised by the auto-ignition velocity, ua, and  is the acoustic wave residence time in the auto-igniting hot spot, normalised by the excitation time, e  .…”

Section: Introductionmentioning

confidence: 99%

Deflagrative, auto-ignitive, and detonative propagation regimes in engines

Bates

2017

Combustion and Flame

Self Cite

The paper presents a novel overall quantitative description of the major regimes of engine combustion, covering the influences of both turbulence and auto-ignition parameters on burn rates and flame extinctions. It involves two separate, yet interconnected, correlation diagrams. The first involves the normalised turbulent burning velocity, the Karlovitz stretch factor the strain rate Markstein number, and also includes possible the relative auto-ignitve burn rates. The second is a complementary correlating