Combustion MCQ

The complete combustion reaction of methane and oxygen: CH4 + 2 O2 = CO2 + 2 H2O is

a global equation behind which many elementary processes are hidden

The sequence of carbon containing intermediates involved in the oxidation of methane to CO2 is

CH4 - CH3 - CH3O - CH2O - CHO - CO - CO2

An endothermic process is a process

which absorbs heat and whose enthalpy of reaction is positive

Combustion reactions are globally

exothermic

It is possible to carry out combustion in difluorine (F2)

true

In this course, the equivalence of ratio of a mixture is given by the ratio

(quantity of fuel / quantity of oxidizer)_studied mixture / (quantity of fuel / quantity of oxidizer)_stoichiometric mixture

An oxidizing – fuel mixture with an equivalence ratio equal to 2 is

a rich mixture and a mixture with excess of fuel over stoichiometry

An Ostwald diagram

is valid for a given fuel

An equivalence ratio (or an air factor) equals to 1 allows complete combustion

false

1 kilowatt-hour (kWh)

corresponds to 3.6MJ and is an energy

What are NASA polynomials used for

calculate the thermodynamic properties of a species

In the NASA polynomial formalism, the first seven coefficients are used to calculate the thermodynamic properties of species

at high temperature

Consider the reaction between one mole of H2 and one mole of O2. The right expression of the complete reaction of combustion is:

H2 + O2 = H2O + 0.5 O2

An adiabatic flame temperature is calculated at

constant pressure

When calculating an adiabatic flame temperature in air

we need the Cp of the products and the nitrogen, and the enthalpies of formation of reactants and products

The adiabatic explosion temperature is

higher than flame adiabatic temperature

The order of magnitude of a flame temperature in air is

2000 - 2500 K

When a combustion reaction is carried out in pure oxygen

the adiabatic flame temperature is higher than in air

For lean mixtures (when the equivalence ratio is less than 1) the decrease in temperature observed is due to

the effect of dilution by atmospheric nitrogen and an excess of oxygen

Why does the calculation by hand of the adiabatic flame temperature of a fuel in air give a different result from the Gaseq software

because the reaction is considered to be complete whereas it is not true and because one can consider that N2 is inert

Gaseq software uses thermodynamic properties stored as NASA polynomials in a text file

true

In Gaseq, the value of the adiabatic flame temperature of a fuel depends on the products considered

true

To lower the flame temperature in a process operating under oxycombustion, __________ can be introduced at the inlet of the combustion chamber

water

The enthalpy of a combustion reaction

changes little with temperature

We want to calculate the adiabatic flame temperature of one mole of methane in the presence of 2 moles of O2 in the air. The reaction to consider is

CH4 + 2 O2 + 7.52 N2 = CO2 + 2 H2O + 7.52 N2

I can carry an acetylene cylinder horizontally

false

A value of calorific power is a

energy per unit volume or mass

The HHV (high heating value) is

greater than the LHV (lower heating value)

For a fuel in the gaseous state under standard conditions, the LHV is equal to the opposite of the combustion reaction enthalpy if we consider that the reaction is ___________ and ________.

complete and total

The LHV of biogas is higher than that of natural gas

true

The effective LHV of wood

decreases with residual water content

It is better to burn wet wood than dry wood

false

The octane rating of a gasoline fuel characterizes the fuel's propensity to self-ignite

true

E10 fuel is more economically advantageous than Eurosuper fuel

false

I have a vehicle that runs on 100% ethanol fuel. I should fill it up

more often

A reaction whose enthalpy is negative

gives off heat and is an exothermic reaction

A mixture containing 4 moles of oxygen and 1 mole of methane is

a mixture with an equivalence ratio of 0.50

The adiabatic flame temperature of acetylene in O2 is calculated using

the Cp of the products

Calorific power is expressed in

J/kg and J/m³

A gasoline engine can be considered as

a closed reactor with a variable volume

The ideal thermodynamic cycle of a diesel engine consists of

two isentropic transformations, one isobaric and one isochoric

The Cp of a fuel

increases with temperature

The HHV is calculated by

LHV - latent heat of vaporisation and LHV + latent heat of condensation

For rich mixtures (when the equivalence ratio is higher than 1), the decrease in adiabatic flame temperature is due to

deficit in oxygen and an incomplete reaction

Which of these units correspond to energies

J and KWh