3 (a) Briefly describe what is meant by engine knock and why it is detrimental to the operation of a spark ignition (SI) engine.

(b) High Octane fuels are used in SI engines to help avoid knock. Define what is meant by the terms Research Octane Number (RON) and Motor Octane Number (MON). Qualitatively describe how these quantities are related to auto-ignition processes when referring to a fuel-air mixture and thus how they relate to the knocking potential of a fuel.

(c) Define the term minimum ignition energy (MIE). Qualitatively explain how the AIT for a fuel air mixture varies with the following conditions for both methane and larger hydrocarbons: (i) Stoichiometry (ii) Temperature (iii) Pressure (iv) Gas velocity

(d) Define the meaning of the burning velocity for a laminar flame. How are laminar burning velocity, gas speed and flame speed related?

(e) Define what is meant by quench distance (QD) for a fuel air mixture and briefly describe the principle of operation of a flame trap.

(f) What is a typical burning velocity and QD for natural gas burning under stoichiometric conditions? Using this information, design a premixed laminar flame burner (fuel and air flow rates and number of burner holes) for natural gas with a thermal output of 20 kW that must not have a risk of flash back into the upstream premixing passage. You may assume in your calculations an overall efficiency of 93% and an NCV for natural gas of 50 MJ/kg. The density of the mixture can be taken to be 1.2 kg/m3 and stoichiometric conditions can be assumed. Explain your reasons for any further assumptions made.