THERMODYNAMICS MANUAL / B- TECH MECH. / MEASURE THE FLASH POINT

AIM: - TO MEASURE THE FLASH POINT OF GIVEN FUEL

APPARATUS: - FLASH POINT OF OPERATOR

THEORY (FLASH & FIRE POINT):-

FLASH POINT OF LUBRICATING OIL IS THE TEMPERATURE AT WHICH IT WILL GIVE OFF SUFFICIENT VAPORS TO FORM A COMBUSTIBLE MIXTURE WITH AIR. IT WILL IGNITE MOMENTARILY WHEN A FLAME IS BROUGHT CLOSE TO IT. IN THIS CASE FIRE ONLY TAKES PLACE AND THE EXTINGUISHES BUT DOES NOT BURN CONTINUOUSLY. PRACTICALLY ALL LUBRICATING OIL HAVE FLASH POINTS SUFFICIENTLY HIGH TO ELIMINATE FIRE HAZARDS IN STORAGE AS WELL AS DURING USE. FLASH POINT DETERMINATION IS ONE OF THE IMPORTANT TESTS, THE OMISSION OF WHICH MAY CAUSE A SERIOUS FIRE HAZARD. THE MINIMUM FLASH POINT FOR IC ENGINE LUBRICATING OILS VARIES FROM 175 DEGREE C TO 250 DEGREE C. IF THE FLASH POINT IS TOO LOW THE OIL WILL BURN, DEPOSITING CARBON AROUND THE PISTON RINGS.

FIRE POINT OF LUBRICATING OIL IS THE TEMPERATURE AT WHICH IT WILL CONTINUE TO BURN AFTER THE INFLAMMABLE VAPORS AIR MIXTURE IS IGNITE. AS A GENERAL RULE THIS EVENT TAKES PLACE WHEN THE TEMPERATURE IS RAISED 30 DEGREE C TO 45 DEGREE C ABOVE THE FLASH POINT. FIRE POINT IN CONJUNCTION WITH THE FLASH POINT IS A ROUGH INDICATION OF THE VOLATILITY OF OIL.

THE FLASH & FIRE POINTS ARE FOUND UNDER TWO CONDITIONS OF SURROUNDINGS I.E. OPEN & CLOSED. IN OPEN CUP, THE OIL IS HEATED WITH THE UPPER SURFACE OF THE OIL EXPOSED TO ROOM. FOR OPEN CUP, FLASH POINT IS HIGHER DUE TO COOL AIR CURRENTS INSIDE THE ROOM, THEN FOR THE CLOSED CUP FLASH POINT, OIL IS HEATED IN A CONFINED SPACE.

THE DETERMINATION OF FLASH & THE FIRE POINT IS MADE WITH THE HELP OF MANY DIFFERENT TYPES OF APPARATUS MOST POPULAR IN INDIA IS PENSKY-MARTEN FLASH POINT APPARATUS.

PROCEDURE: -

TO CARRY OUT THE TEST THE CUP IS FILLED WITH THE NECESSARY AMOUNT OF OIL UP TO THE MARK & IS THEN HEATED SUCH THAT THE RATE OF HEATING SHOULD BE NEARLY 5DEGREE C PER MINUTE. THE OIL IS HEATED 10 DEGREE C BELOW THE FLASH POINT AND IS CONTINUOUSLY STIRRED AT THE RATE OF ONE OR TWO REVOLUTIONS PER SECOND BETWEEN TRIALS. THE TEST FLAME IS APPLIED AT EVERY 3 DEGREE C RISE IN TEMPERATURE. NO STIRRING IS DONE DURING THE APPLICATION OF TEST FLAME. THE FLASH POINT IS THE TEMPERATURE AT WHICH A DISTINCT FLASH IS FIRST SEEN ON THE SURFACE OF THE OIL, WHEN THE TEST FLAME IS APPLIED. THIS METHOD CANNOT GIVE FLASH POINT CLOSER THAN 3DEGREE C. NOW SINCE THE OIL CUP IS COVERED, THE VAPOUR CANNOT ESCAPE AS IT IS FORMED, SO THAT IT IS CALLED THE CLOSED RAISED BY ABOUT 15 DEGREE C

AND IT IS THEN CALLED THE OPEN FLASH POINT. AFTER THE FLASH POINT IS DETERMINED, THE FIRE POINT IS FOUND BY CONTINUING TO HEAT THE OIL AT THE SAME RATE UNTIL THE TEST FLAME IGNITES THE OIL. IF IT CONTINUES TO BURN FOR AT LEAST 5 SECS THEN THIS TEMPERATURE IS TAKEN AS THE FIRE POINT TEMPERATURE. THEN CLOSING COVER PLATE PUTS OUT THE FLAME. AFTER THE FLASH POINT IS DETERMINED, THE FIRE POINT IS FOUND BY CONTINUING TO HEAT THE OIL AT THE SAME RATE UNTIL THE TEST FLAME IGNITES THE OIL. IF IT CONTINUES TO BURN FOR AT LEAST 5 SECS THEN THIS TEMPERATURE IS TAKEN AS THE FIRE POINT TEMPERATURE. THEN CLOSING COVER PLATE PUTS OUT THE FLAME.