IT WILL CAUSE AN ABNORMALLY HIGH PEAK PRESSURE
POWER GENERATION AND SFC WILL IMPROVE AND DROP IN EXHAUST TEMPERATURE.
A HEAVY SHOCK LOAD WILL BE TRANSMITTED TO THE RUNNING GEAR AND BEARINGS WITH A KNOCKING SOUND.
CAUSES OF EARLY IGNITION MAY BE INCORRECT FUEL PUMP TIMING, BROKEN OR WRONGLY SET INJECTOR SPRINGS, INCORRECT FUEL CONDITION, OVERHEATED PART SUCH AS HOT PISTON.
THE SHOCK LOAD AND VIBRATIONS MAY CAUSE DAMAGE
LATE IGNITION :
CAUSES A LOW PEAK PRESSURE WHICH OCCURS WELL AFTER TOP CENTRE OF THE PISTON.
LOSS OF POWER AS FUEL IS NOT BURNED COMPLETELY.
COMBUSTION INCOMPLETE, LOSS OF ENERGY, HIGH EXHAUST TEMP AND SMOKE.
CAUSES- EXCESSIVE INJECTOR SPRING SETTING, POOR ATOMIZATION, HIGH VISCOSITY OR POOR QUALITY OF FUEL, FUEL PUMP LEAKING OR INCORRECTLY TIME, LOW COMPRESSION, INSUFFICIENT SUPPLY OF COMBUSTION AIR, OR UNDER COOLING OF PARTS WITHIN THE CYLINDER.
LOW COMPRESSION
POWER GENERATION WILL BE LESS.
FAULTY COMBUSTION, HIGH EXHAUST TEMPERATURE.
LOW PRESSURES DUE TO LACK OF AIR (TURBOCHARGER FAULTS, CHOKED SCAVENGE PORTS OR INLET VALVE, CHOKED AIR COOLER, CHOKED AIR FILTER).
BLOW PAST FROM WORN OUT OR BROKEN PISTON RINGS, WORN LINER, LACK OF CYLINDER LUBRICATION, STICKING PISTON RINGS.
BLOWPAST CAN CAUSE SCAVENGE FIRE IN 2 STROKE ENGINES AND THERE IS A RISK OF CRANKCASE EXPLOSION IN 4 STROKE ENGINES.
AFTERBURNING
SLOW OR LATE COMBUSTION OF FUEL DURING EXPANSION STROKE OF PISTON.
SHOWN BY A RISE IN THE EXPANSION LINE DURING THE LATER PART OF THE STROKE.
EXHAUST TEMP AND PRESSURE WILL BE HIGH, WITH BURNING FUEL AND CARBON PASSING TO EXHAUST.
THIS MAY DAMAGE THE EXHAUST VALVES AND FOUL THE EXHAUST SYSTEM, CAUSING TURBOCHARGER SURGING OR UPTAKE FIRES.
HIGH TEMP OF LINER CAUSES DETERIORATION OF LUBRICATION AND DAMAGE TO LINER AND PISTON RINGS.
MAY CAUSE BURNING OF PISTON CROWN.
CAUSES OF AFTER BURNING ARE : INCORRECT FUEL PUMP TIMING, FAULTY FUEL INJECTOR, FO TEMP TOO LOW, LACK OF SCAVENGE AIR, POOR COMPRESSION.
eAnd f. CHOCKED INTAKE
LOSS OF POWER,LOW COMPRESSION,HIGH EXHAUST TEMP.
INCOMPLETE COMBUSTION DUE TO INSUFFICIENT AIR.
LACK OF AIR DUE TO TURBOCHARGER FAULTS, CHOKED SCAVENGE PORTS OR INLET VALVE, CHOKED AIR COOLER, CHOKED AIR FILTER.
LEAKING FUEL INJECTOR :
Leaking Fuel Injector will be detected by loss in power, smoke at Exhaust, high exhaust temperature.
Indicator diagram will show fluctuation of pressure during the expansion process due to secondary burning of fuel leaking from injector.
It can lead to loss in power, there may also be a knock or pressure wave.
There can be blow back of hot gases into injector tip, resulting in forming carbon and choking of the atomizer.
To reduce this possibility proper maintenance on fuel pumps and injectors should be carried out. Fuel must be purified, filtered and maintained at correct temperature.
EXHAUST VALVE OPENING
Can be checked by means of light spring indicator card diagram.
This will not give accurate timing check but can be compared with normal diagram or one taken during sea trials.
Early opening :Will cause a loss in power since pressure is released too soon. Results in high exhaust temperature with risk of overheating.
Late Opening : Will reduce the scavenge efficiency by reducing blow down.
Chocked Exhaust – Prevents blow down and recharge of the cylinder with air. Will result in Loss of power, High Exhaust temperature, smoke and surging of turbocharger.
Author AMIT
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