Direct Numerical Simulations (DNS) data of Moderate or Intense Low-oxygen Dilution (MILD) combustion are analysed to identify the contributions of the autoignition and flame modes. This is performed using an extended Chemical Explosive Mode Analysis (CEMA) which accounts for diffusion effects allowing it to discriminate between deflagration and autoignition. This analysis indicates that in premixed MILD combustion conditions, the main combustion mode is ignition for all dilution and turbulence levels and for the two reactant temperature conditions considered. In non-premixed conditions, the preponderance of the ignition mode was observed to depend on the axial location and mixture fraction stratification. With a large mixture fraction lengthscale, ignition is more preponderant in the early part of the domain while the deflagrative mode increases further downstream. On the other hand, when the mixture fraction lengthscale is small, sequential autoignition is observed. Finally, the various combustion modes are observed to correlate strongly with mixture fraction where lean mixtures are more likely to autoignite while stoichiometric and rich mixtures are more likely to react as deflagrative structures.

This paper presents the results of a human-in-the-loop experiment performed to investigate the effects of variations in aircraft short-period mode characteristics on human operators’ manual control behavior. In the experiment, 15 participants performed a tracking task for a factorial variation in both short-period mode natural frequency (five settings) and damping ratio (three settings). The baseline aircraft dynamics were those of a Cessna Citation aircraft, as used in a number of previous experiments, and the variations in short-period dynamics were chosen to span a range of interest with respect to available handling qualities criteria and Maximum Unnoticed Added Dynamics (MUAD) envelopes. To objectively quantify the induced adaptation of manual control behavior, human operator models were fitted to the collected tracking data. In addition to these control behavior measures also subjective ratings of the noticeability of differences with respect to the baseline aircraft were collected. Overall, the results show consistent adaptation of manual control behavior to variations in both short-period parameters and a worsening of task performance with decreased short-period natural frequency and decreased damping ratio settings. In spite of inconsistencies in the subjective rating data, the overall objective adaptation of manual control dynamics correlates with the subjective noticeability ratings, as well as correspondence of the tested configurations with available MUAD envelopes.