Temperature Stratification Induced Ignition Regimes for Gasoline Surrogates at Engine-Relevant Conditions

ABSTRACT

End-gas auto-ignition leading to knocking combustion is one of the major barriers to achieving higher thermal efficiencies in downsized boosted spark-ignition engines. Despite the available framework addressing hotspot-induced ignition (detonation peninsula), a quantitative investigation on hotspot-induced auto-ignition of gasoline surrogates is yet to be done. In particular, the effect of negative temperature coefficient (NTC) chemistry on the distribution of the ignition modes in the detonation peninsula is still missing. Using the established one-dimensional (1D) theoretical and computational framework, the effect of average temperature (including NTC range), initial pressure, and ethanol addition are investigated. Moreover, appearance of NTC chemistry-related events i.e. coolspots, secondary ignition kernels, and off-centered ignition are analyzed using 1D simulations. The results are as follows. 1) NTC chemistry affects the distribution of ignition regimes in detonation peninsula and the dynamics of the front propagation via altering the reactivity gradient. 2) NTC chemistry increases the temperature gradient range associated with the detonation regime. 3) NTC may inhibit detonation development by simultaneously promoting the spontaneous/supersonic ignition modes. 4) An ethanol blend decreases the knock propensity; however, lower ignitability may promote detonation development and the appearance of strong shock waves. 5) Finally, detonation may result in a normal knock at lower initial pressures (20 bar). However, at elevated initial pressures (50 bar), detonation is noted to yield pressure intensities resembling super-knock.

KEYWORDS:

• Combustion modes
• temperature stratification
• gasoline surrogates
• spark ignition engines
• knock

Acknowledgement

We would like to acknowledge Aalto University and CSC (Finnish IT Center for Science) for providing the computational resources.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The present study has been financially supported by Neste Corporation, Finland, and the Academy of Finland [grant numbers 318024 and 332784].