b$)$ Fuels for Diesel engines undergo various processes from the instant fuel emerges from the nozzle holes of a direct injector to the moment when ignition of the fuel occurs.

i$)$ Sketch a typical diesel combustion heat release rate plot.

$[5$ marks$]$

ii$)$ With reference to your answer in part b i$)$ of this question identify the physical processes experienced by a fuel during the ignition delay period.

$[5$ marks$]$

iii$)$ With reference to your answer in part b i$)$ of this question identify the chemical processes experienced by a fuel during the ignition delay period.

$[5$ marks$]$

$\backslash$table$[[$Engine displacement,$25601\mathrm{.}8,$litres$],[$Engine rotational speed, N$,87,$rpm$],[$Engine brake power,$35,000,$kW$],[$Engine friction mean effective pressure,$3\mathrm{.}6,$bar$],[\backslash$table$[[$The air mass flowrate supplied to the engine by the$],[$supercharger compressor$]],48,$kg$/$s$],[$Engine thermal efficiency,$42,\%],[$Diesel fuel calorific value,$44\mathrm{.}8,$MJ$/$kg$],[$Air pressure at turbocharger exit and engine intake, p$02,2\mathrm{.}9,$bar$],[$Air temperature at turbocharger exit and engine intake, T$02,238,\backslash$deg C$],[$Air temperature at intake of turbocharger, T$01,25,\backslash$deg C$],[$Atmospheric pressure, p$01,1\mathrm{.}01,$bar$],[$Specific gas constant for air, Ra$,287,$J$/($kgK$)],[$Compressor isentropic efficiency,$0\mathrm{.}81,],[$Ratio of specific heats for air, Ya$,1\mathrm{.}4,]]$

Table $2.$ Data for two stroke Diesel engine

TURN OVER

MECH$0051$ MAIN $20212022$

$4$

The compressor isentropic power $(\{$:$W_c^{})$ is given by:

$W_c^{}{?}^{\text{'}}=m_s^{}{R}_a{T}_{01}\frac{{}_a}{{}_a-1}[1-(\frac{p_{02\text{'}}}{p_{01}}{)}^{\frac{{}_a-1}{{}_a}}]$

The turbine isentropic power $(W_t^{})$ is given by:

$W_t^{}{?}^{\text{'}}=m_s^{}{R}_a{T}_{03}\frac{{}_a}{{}_a-1}[1-(\frac{p_{041}}{p_{03}}{)}^{\frac{{}_a-1}{{}_a}}]$

All symbols have their usual meanings.