10 02 21 quiz

Pagina 1

10/02/21 The EIVC (early intake valve closing) is useful to: 1) Optimize the valve overlap period 2) Control the air mass flow rate without closing the throttle valve 3) Increase the gas exchange work 4) Achieve a sort of super-charging effect The (open valve) wave effect in the intake system: 1) Is always beneficial, due to the increase of volumetric efficiency 2) Can be correctly exploited at low engine speeds with long pipes 3) Must be tuned to achieve a compression wave on the exhaust port 4) Does not depend on the speed of sound in the pipe Constant pressure turbocharging: 1) Determines significant fluctuations of the turbine efficiency 2) Requires a double-entry compressor 3) Increases the pressure oscillations in a large volume exhaust manifold 4) Suffers from the “turbo-lag” issue The VGT is a generally better solution to: 1) Reduce cost and increase realiability 2) Achieve a complete conversion of pollutant emissions in the after-treatment system 3) Guarantee the proper level of boost pressure for different engine speeds 4) Avoid the EGR recirculation The risk of knock in a SI engine: 1) Becomes higher when the flame front velocity is increased 2) Is increased by reducing the compression ratio 3) Is mitigated by injection of water in the chamber 4) Is reduced by lowering the octane number of the fuel In a SI engine the highest production on unburnt HC in the chamber is achieved: 1) For an equivalence ratio greater than 1 2) For an equivalence ratio lower than 1 3) For an equivalence ratio equal to 1 4) For an equivalence ratio equal to 0.5 In a CI engine an EGR rate = 20%, if compared with no EGR: 1) Generally increases the turbine power 2) Determines an increase of soot emissions 3) Can be achieved only by dual stage turbocharging 4) Allows a significant…