An essential requirement for investigation of poor performance of the main engine is to study the indicator cards along with their drawcards , measure and estimate the power developed in each unit. Where the performance of scavenge and exhausting are doubtful, their light spring diagrams must also be taken for investigation. In those units where compression is doubtful their compression cards must also be taken After analysing and confirming the faults the general process of improving performance is summarised as given under.
The main consideration for the improvement of thermal efficiency in an engine are :
- Compression ratio or compression pressure
- Quality and optimization of combustion
- Scavenge efficiency
Compression ratio:- The compression ratio in an engine is fixed by design and cannot be changed. However the compression ratio falls short or deteriorates by liner wear and wear and tear of piston rings. If liner condition is maintained and piston ring wear and tear is corrected by suitable renewal, the required compression is restored
Combustion quality :- Is governed by the correct metering of the fuel combined with the requirements of atomisation, penetration and turbulence properly balanced results in optimization of combustion. Practically this condition is achieved by proper maintenance and adjustment of the fuel injectors coupled with efficient operation of the fuel pumps properly timed and metered to suit the load conditions
Scavenge efficiency is essential because it governs the volumetric efficiency of the air intake and , without contamination of the air by the exhaust gases. This requirement is practically achieved by the efficient operation of the turbo charger leading to optimization of scavenge pressure and temperature with clean scavenge ports to give free flow of the scavenge air into the cylinder and finally the efficient operation of the exhaust valves properly timed to evacuate the exhaust so fresh air can fill the cylinder without contamination
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