During the valve overlap period, the exhaust pressure of a turbocharged four-stroke/cycle diesel engine must be less than the intake manifold pressure to ensure ______.A.effective cylinder scavenging and coolingB.constant pressure from the turbochargersC.cooler operation of the exhaust systemD.effective constant pressure for turbocharger operation
During the valve overlap period, the exhaust pressure of a turbocharged four-stroke/cycle diesel engine must be less than the intake manifold pressure to ensure ______.
A.effective cylinder scavenging and cooling
B.constant pressure from the turbochargers
C.cooler operation of the exhaust system
D.effective constant pressure for turbocharger operation
相关考题：
Any increase in the exhaust back pressure of a four-stroke/cycle diesel enginewill( ).A.reduce engine horsepower outputB.aid in silencing the exhaust noiseC.increase the mean effective pressureD.contribute to effective cylinder scavenging
单选题The period of valve overlap is when （）.Athe inlet valve is openBthe exhaust valve is openCboth valves are closeDboth valves are open
单选题Valve overlap is the period during which （）.Athe inlet valve is openBthe exhaust valve is openCboth valves are closedDboth valves are open
单选题A two-stroke diesel engine exhaust temperature will be lower than a four-stroke diesel engine of the same displacement because the （） (1) MEP is lower and the scavenging air is cooling the exhaust gases (2) valve overlap in a four-strokeA(1) only is correctB(2) only is correctCboth (1) and (2) are correctDNeither (1) or (2) are correct
单选题The size of the exhaust valve opening is （）Amost critical in a four-stroke cycle diesel engineBmost critical in a two-stroke/cycle diesel engineCmost critical in a four-stroke/cycle diesel engine if it is turbochargedDof equal importance in a two-stroke/cycle diesel engine as in a four-stroke/cycle diesel engine
单选题During the fuel injection period, fuel pressure must exceed cylinder gas pressure to （）.Aensure penetration and distribution of the fuel in the combustion chamberBensure the needle valve is flushed clean during each injectionCprevent combustion gas blowback into the open needle valveDprevent reflected pressure waves when the needle valve closes
单选题The exhaust system for a turbocharged two-stroke/cycle diesel engine functions to（）Adischarge exhaust gases and smokeBfurnish energy to the turbochargerCreduce engine room noiseDall of the above
单选题High exhaust temperatures from all of cylinder of a turbocharged, four-stroke/cycle diesel engine can be caused by an（）Ainoperative turbochargerBinadequate fuel supplyCoverload on one cylinderDunequal load distribution
单选题In a closed cooling system for a turbocharged, four-stroke/cycle diesel engine, fluctuating water pressure can be caused by （）Aimproper venting of the cooling systemBcarrying the expansion tank water level too highCa totally clogged impeller in the cooling water pumpDan incorrectly set cooling system temperature control
单选题During the valve overlap period, the exhaust pressure of a turbochargers, four-stroke/cycle diesel engine must be less than the intake manifold pressure to ensure （）Aeffective cylinder scavenging and coolingBconstant pressure from the turbochargersCcooler operation of the exhaust systemDeffective constant pressure for turbocharger operation
单选题Proper lubrication of the main bearing is more easily obtained in a single acting four-stroke/cycle diesel engine than in a single acting two-stroke/cycle diesel engine because （）Abearing pressure in a four-stroke/cycle acting single diesel engine is continually reversedBbearing pressure in a two-stroke/cycle single acting diesel engine is continually reversedCthe maximum bearing pressure is higher in a single acting two-stroke/cycle diesel engineDtwo-stoke/cycle diesel engines require more complicated lubrication piping
单选题Scavenging in a four-stroke/cycle diesel engine occurs during the （）.Alast part of the exhaust stroke, and the first part of the intake strokeBlast part of the intake stroke onlyCearly part of the injection stroke onlyDearly part of the power stroke
单选题A turbocharged diesel engine will have an intake manifold pressure（）Aconstantly decreasing as engine load increaseBconstantly increasing as the amount of supercharging increasesCapproximately equal to exhaust manifold pressure at all timesDapproximately equal to atmospheric pressure at all times
单选题Exhaust valve openings in a diesel engine cylinder head are made as large as practical to （）Aincrease back pressure during the exhaust processBfacilitate periodic replacement of the valvesCreduce the pumping loss associated with scavengingDreduce tension on valve springs
单选题Clearance volume scavenging in a turbocharged, four-stroke/cycle diesel engine is accomplished （）.Aduring the valve overlap periodBwith only the exhaust valve openCat a pressure below atmosphericDwithout cooling the cylinders or pistons
单选题In an engine with air inlet valve and exhaust valve on its cylinder heads the fresh air will enter into the cylinder （） and the gases exhaust （）, there being an adequate overlap between the inlet opening and the exhaust closing.Adownwards；upwardsBupwards；downwardsCdownwards；downwardsDupwards；upwards
单选题Any increase in the exhaust back pressure of a four-stroke/cycle diesel engine will （）.Areduce engine horsepower outputBaid in silencing the exhaust noiseCincrease the mean effective pressureDcontribute to effective cylinder scavenging
单选题Which of the following statements is correct regarding a turbocharged four-stroke/cycle diesel generator?（）AAt zero load the intake manifold pressure is greater than the exhaust manifold pressureBAt full load the intake manifold pressure and exhaust manifold pressure are equalCAt full load the intake manifold pressure is less than the exhaust manifold pressureDAt full load the intake manifold pressure is greater than the exhaust manifold pressure
单选题A turbocharged, four-stroke/cycle diesel engine has a larger valve overlap than a naturally aspirated four-stroke/cycle diesel engine, in order to in crease the （）.Atemperature of the exhaust gasesBenergy supplied to the turbochargerCair pressure to the intake manifoldDpurge of exhausted gases from the cylinders
单选题Turbocharged four-stroke/cycle diesel engines utilize valve overlap for（）.Aimproving cylinder scavengingBpreheating the combustion chamberCreducing air charge densityDpreventing valve wear
单选题Scavenging in a turbocharged, four-stroke/cycle diesel engine is accomplished（）Aduring the valve overlap periodBwith only the exhaust valve openCat a pressure below atmosphericDwithout cooling the cylinders or pistons
单选题A four-stroke cycle, turbocharged, 1000 horsepower diesel engine has been operating under loadThe load suddenly increases, causing excessive black exhaust smoke, and a rapid rise in the lube oil temperatureIn response to this condition, you should:（）Areduce loadBcheck your exhaustCadjust cooling water temperatureDincrease lube oil flow
单选题Which of the listed components is considered to separate the high pressure side of a refrigeration cycle from the low pressure side of the cycle?（）AThe condenser and the expansion valveBThe king valve and the solenoid valveCThe compressor and the expansion valveDThe condenser and the solenoid valve
单选题A four-stroke/cycle, 1000horsepower diesel engine fails to start at normal cranking speed with normal fuel pressure and ambient temperatureThe reason for the failure could be（）Aglazed liners or pistonsBhigh lube oil pressureCexcessive compression ratioDworn valve seats and valves
单选题If the engine is naturally aspirated, or is a small high-speed type with a centrifugal turbocharger, the period of valve overlap（）,ie when both valves are（）, will be and the exhaust valve will close some 10°top dead canter（）.Aopen；short；afterBclosed；short；afterCopen；long；beforeDclosed；long；before
单选题In a turbocharged four-stroke/cycle diesel engine, the exhaust valve remains open until after top dead center and the intake valve opens before top dead center to（）.Aproduce a scavenging effect in the combustion spaceBequalize cylinder and exhaust manifold pressuresCalleviate the difference in valve size between the intake and exhaustDflush out condensate that collects after each compression stroke
单选题A piston in a four-stroke/cycle diesel engine makes four strokes during each （）.Acrankshaft revolutionBmechanical cycle of operationCperiod of two combustion cyclesDcycle of two events