POWER ENGINEERING EXAM QUESTIONS And
CORRECT Answers
HEAT ENGINE - CORRECT ANSWERS DEVICE THAT TAKES IN ENERGY BY HEAT AND,
OPERATING IN A CYCLIC PROCESS, EXPELS A FRACTION OF THAT ENERGY BY MEANS OF WORK.
INTAKE STROKE - CORRECT ANSWERS THE PISTON MOVES DOWNWARD AND A GASEOUS
MIXTURE OF AIR AND FUEL IS DRAWN INTO THE CYLINDER AT ATMOSPHERIC PRESSURE. THAT IS
THE ENERGY INPUT PART OF THE CYCLE: ENERGY ENTERS THE SYSTEM (THE INTERIOR OF THE
CYLINDER) BY MATTER TRANSFER AS POTENTIAL ENERGY STORED IN THE FUEL. IN THIS
PROCESS, THE VOLUME INCREASES FROM V2 TO V1. THIS APPARENT BACKWARD NUMBERING
IS BASED ON THE COMPRESSION STROKE (PROCESS 2 BELOW), IN WHICH THE AIR[1]FUEL
MIXTURE IS COMPRESSED FROM V1 TO V2.
COMPRESSION STROKE - CORRECT ANSWERS THE PISTON MOVES UPWARD, THE AIR-FUEL
MIXTURE IS COMPRESSED ADIABATICALLY FROM VOLUME V1 TO VOLUME V2, AND THE
TEMPERATURE INCREASES FROM TA TO TB. THE WORK DONE ON THE GAS IS POSITIVE, AND ITS
VALUE IS EQUAL TO THE NEGATIVE OF THE AREA UNDER THE CURVE AB.
COMBUSTION - CORRECT ANSWERS OCCURS WHEN THE SPARK PLUG FIRES. THAT IS NOT
ONE OF THE STROKES OF THE CYCLE BECAUSE IT OCCURS IN A VERY SHORT TIME INTERVAL
WHILE THE PISTON IS AT ITS HIGHEST POSITION. THE COMBUSTION REPRESENTS A RAPID
ENERGY TRANSFORMATION FROM POTENTIAL ENERGY STORED IN CHEMICAL BONDS IN THE
FUEL TO INTERNAL ENERGY ASSOCIATED WITH MOLECULAR MOTION, WHICH IS RELATED TO
TEMPERATURE.
POWER STROKE - CORRECT ANSWERS THE GAS EXPANDS ADIABATICALLY FROM V2 TO V1.
THIS EXPANSION CAUSES THE TEMPERATURE TO DROP FROM TC TO TD. WORK IS DONE BY THE
GAS IN PUSHING THE PISTON DOWNWARD, AND THE VALUE OF THIS WORK IS EQUAL TO THE
AREA UNDER THE CURVE CD.
, RELEASE - CORRECT ANSWERS RESIDUAL GASES OCCURS WHEN AN EXHAUST VALVE IS
OPENED. THE PRESSURE SUDDENLY DROPS FOR A SHORT TIME INTERVAL. DURING THIS TIME
INTERVAL, THE PISTON IS ALMOST STATIONARY AND THE VOLUME IS APPROXIMATELY
CONSTANT. ENERGY IS EXPELLED FROM THE INTERIOR OF THE CYLINDER AND CONTINUES TO BE
EXPELLED DURING THE NEXT PROCESS.
EXHAUST STROKE - CORRECT ANSWERS THE PISTON MOVES UPWARD WHILE THE
EXHAUST VALVE REMAINS OPEN. RESIDUAL GASES ARE EXHAUSTED AT ATMOSPHERIC
PRESSURE, AND THE VOLUME DECREASES FROM V1 TO V2. THE CYCLE THEN REPEATS.
IF THE AIR-FUEL MIXTURE IS ASSUMED TO BE AN IDEAL GAS, THE EFFICIENCY OF THE OTTO
CYCLE IS - CORRECT ANSWERS 𝑒 = 1 − 1 /[𝑉1⁄𝑉2 ]^𝛾−1
DIESEL ENGINE - CORRECT ANSWERS 1. DO NOT EMPLOY A SPARK PLUG.
2. THE COMPRESSION RATIO IS GREATER THAN GASOLINE ENGINE.
3. AIR IN THE CYLINDER IS COMPRESSED TO A VERY SMALL VOLUME, AND, AS A CONSEQUENCE,
THE CYLINDER TEMPERATURE AT THE END OF THE COMPRESSION STROKE IS VERY HIGH.
4. THE TEMPERATURE IS HIGH ENOUGH FOR THE AIR-FUEL MIXTURE TO IGNITE WITHOUT THE
ASSISTANCE OF A SPARK PLUG.
5. DIESEL ENGINES ARE MORE EFFICIENT THAN GASOLINE ENGINES BECAUSE OF THEIR GREATER
COMPRESSION RATIOS AND RESULTING HIGHER COMBUSTION TEMPERATURES.
MAIN ENGINE COMPONENT PARTS - CORRECT ANSWERS 1. CYLINDER BLOCK
2. CYLINDER
CORRECT Answers
HEAT ENGINE - CORRECT ANSWERS DEVICE THAT TAKES IN ENERGY BY HEAT AND,
OPERATING IN A CYCLIC PROCESS, EXPELS A FRACTION OF THAT ENERGY BY MEANS OF WORK.
INTAKE STROKE - CORRECT ANSWERS THE PISTON MOVES DOWNWARD AND A GASEOUS
MIXTURE OF AIR AND FUEL IS DRAWN INTO THE CYLINDER AT ATMOSPHERIC PRESSURE. THAT IS
THE ENERGY INPUT PART OF THE CYCLE: ENERGY ENTERS THE SYSTEM (THE INTERIOR OF THE
CYLINDER) BY MATTER TRANSFER AS POTENTIAL ENERGY STORED IN THE FUEL. IN THIS
PROCESS, THE VOLUME INCREASES FROM V2 TO V1. THIS APPARENT BACKWARD NUMBERING
IS BASED ON THE COMPRESSION STROKE (PROCESS 2 BELOW), IN WHICH THE AIR[1]FUEL
MIXTURE IS COMPRESSED FROM V1 TO V2.
COMPRESSION STROKE - CORRECT ANSWERS THE PISTON MOVES UPWARD, THE AIR-FUEL
MIXTURE IS COMPRESSED ADIABATICALLY FROM VOLUME V1 TO VOLUME V2, AND THE
TEMPERATURE INCREASES FROM TA TO TB. THE WORK DONE ON THE GAS IS POSITIVE, AND ITS
VALUE IS EQUAL TO THE NEGATIVE OF THE AREA UNDER THE CURVE AB.
COMBUSTION - CORRECT ANSWERS OCCURS WHEN THE SPARK PLUG FIRES. THAT IS NOT
ONE OF THE STROKES OF THE CYCLE BECAUSE IT OCCURS IN A VERY SHORT TIME INTERVAL
WHILE THE PISTON IS AT ITS HIGHEST POSITION. THE COMBUSTION REPRESENTS A RAPID
ENERGY TRANSFORMATION FROM POTENTIAL ENERGY STORED IN CHEMICAL BONDS IN THE
FUEL TO INTERNAL ENERGY ASSOCIATED WITH MOLECULAR MOTION, WHICH IS RELATED TO
TEMPERATURE.
POWER STROKE - CORRECT ANSWERS THE GAS EXPANDS ADIABATICALLY FROM V2 TO V1.
THIS EXPANSION CAUSES THE TEMPERATURE TO DROP FROM TC TO TD. WORK IS DONE BY THE
GAS IN PUSHING THE PISTON DOWNWARD, AND THE VALUE OF THIS WORK IS EQUAL TO THE
AREA UNDER THE CURVE CD.
, RELEASE - CORRECT ANSWERS RESIDUAL GASES OCCURS WHEN AN EXHAUST VALVE IS
OPENED. THE PRESSURE SUDDENLY DROPS FOR A SHORT TIME INTERVAL. DURING THIS TIME
INTERVAL, THE PISTON IS ALMOST STATIONARY AND THE VOLUME IS APPROXIMATELY
CONSTANT. ENERGY IS EXPELLED FROM THE INTERIOR OF THE CYLINDER AND CONTINUES TO BE
EXPELLED DURING THE NEXT PROCESS.
EXHAUST STROKE - CORRECT ANSWERS THE PISTON MOVES UPWARD WHILE THE
EXHAUST VALVE REMAINS OPEN. RESIDUAL GASES ARE EXHAUSTED AT ATMOSPHERIC
PRESSURE, AND THE VOLUME DECREASES FROM V1 TO V2. THE CYCLE THEN REPEATS.
IF THE AIR-FUEL MIXTURE IS ASSUMED TO BE AN IDEAL GAS, THE EFFICIENCY OF THE OTTO
CYCLE IS - CORRECT ANSWERS 𝑒 = 1 − 1 /[𝑉1⁄𝑉2 ]^𝛾−1
DIESEL ENGINE - CORRECT ANSWERS 1. DO NOT EMPLOY A SPARK PLUG.
2. THE COMPRESSION RATIO IS GREATER THAN GASOLINE ENGINE.
3. AIR IN THE CYLINDER IS COMPRESSED TO A VERY SMALL VOLUME, AND, AS A CONSEQUENCE,
THE CYLINDER TEMPERATURE AT THE END OF THE COMPRESSION STROKE IS VERY HIGH.
4. THE TEMPERATURE IS HIGH ENOUGH FOR THE AIR-FUEL MIXTURE TO IGNITE WITHOUT THE
ASSISTANCE OF A SPARK PLUG.
5. DIESEL ENGINES ARE MORE EFFICIENT THAN GASOLINE ENGINES BECAUSE OF THEIR GREATER
COMPRESSION RATIOS AND RESULTING HIGHER COMBUSTION TEMPERATURES.
MAIN ENGINE COMPONENT PARTS - CORRECT ANSWERS 1. CYLINDER BLOCK
2. CYLINDER
