Answer
Ans: Shop trial: The purpose of the works trials is to verify design premises such as power, safety against fire, adherence to approved limits (e.g. maximum pressure), and functionality and to establish reference values or base lines for later reference in the operational phase.
NOx technical file is made in shoptrial .
Records
The following environmental test conditions are to be recorded:
- Ambient air temperature
- Ambient air pressure
- Atmospheric humidity
For each required load point, the following parameters are normally to be recorded:
- Power and speed
- Fuel index (or equivalent reading)
- Maximum combustion pressures (only when the cylinder heads installed are designed for such measurement).
- Exhaust g as temperature before turbine and from each cylinder - Charge air temperature
- Charge air pressure
- Turbocharger speed
--Calibration records for the instrumentation are, upon request, to be presented to the attending Surveyor. --For all stag es at which the engine is to be tested, the pertaining operational values are to be measured and recorded by the engine manufacturer. All results are to be compiled in an acceptance protocol to be issued by the engine manufacturer. This also includes crankshaft deflections if considered necessary by the engine designer. --In each case, all measurements conducted at the various load points are to be carried out at steady state operating conditions. However, for all load points provision should be made for time needed by the Surveyor to carry out visual inspections. The readings for MCR, i.e. 100% power (rated maximum continuous power at corresponding rpm) are to be taken at least twice at an interval of normally 30 minutes.
Test loads for various engine applications are given below. In addition, the scope of the trials may be expanded depending on the engine application, service experience, or other relevant reasons.
Note: Alternatives to the detailed tests may be agreed between the manufacturer and the Society when the overall
scope of tests is found to be equivalent.
3.3.2 Propulsion engines driving Propeller or impeller only.
A) 100% power (MCR) at corresponding speed no: at least 60 min.
B) 110% power at engine speed 1.032 no: Records to be taken after 15 minutes or after steady conditions
have been reached, whichever is shorter.
Note: Only required once for each different engine/Turbocharger configuration.
C)Approved intermittent overload (if applicable): testing for duration as agreed with the manufacturer. D) 90% (or
normal continuous cruise power), 75%, 50% and 25% power in accordance with the nominal Propeller curve, the sequence to be selected by the engine manufacturer.
E) Reversing manoeuvres (if applicable).
Note: After running on the test bed, the fuel delivery system is to be so adjusted that overload power cannot be given in service, unless intermittent overload power is approved by the Society. In that case, the fuel delivery system is to be blocked to that power.
Integration tests For electronically controlled engines, integration tests are to be made to verify that the response of the complete mechanical, hydraulic and electronic system is as predicted for all intended operational modes and the tests considered as a system are to be carried out at the works. If such tests are technically unfeasible at the works, however, these tests may be conducted during seatrial. The scope of these tests is to be agreed with the Society for selected cases based on the FMEA required in UR M44.
Component inspections Random Checks of components to be presented for inspection after works trials are left to the discretion of each Society.
Maker has to prove the engine:-
Ø MCR of engine (Power & RPM) + Fuel consumption Ø Minimun fuel consumption
Ø Min. firing RPM for the engine
Ø Transient overload condition
Ø Other associated parameters (temp. , Pressure etc.)
Scope test bed trial:-
Ø @ 25%, 50%, 75% MCR
Ø Matching of Turbocharger to engine Ø NOx measurement (NOx Tech. file)
Shop trial is carried out in the testbed with the help of water dynamo-meter and no Propeller attached. Power is calculated with the formula
P = τ x ω, T= Torque and ω = Angular velocity
In shoptrial we will be calculating power we vary the torque while angular velocity remains constant
By controlling the amount of water flow to dynamo meter we control the torque
Here we will use minimum firing rpm which will be lower than dead slow. The Minimum RPM Depends upon the:- A. Hydrodynamic oil Film- When journal rotates in bearing then it will set up a hydrodynamic film Load on hydrodynamic film , P * pi/4*d 2
Where P = combustion pressure This much load (force)has to be supported by hydro-dynamic film so it has to generate that much of the pressure to support that load .There will be time when angular speed will not be enough to take the load , if we reduce the angular speed so that we can decide minimum RPM
B. Reliability of the Engine- when we reduce the RPM we actually reduce fuel to engine ie We reducing the MEP When RPM reduces heat of compression also reduces , Heat of compression must always remain over and above the auto ignition temp of the fuel So there is min rpm required for fuel to catch the fire and even if it catch fire it may not be able to produce sufficient torque to turn the engine.
C.Vibration in Engine- Engine is tuned closer to service speed so we reduce the RPM until which vibration are acceptable as described above minimum RPM will be Confirmed in Shoptrial.
Further ,Shoptrials are Manufacturers specific in which he has to prove what he said about the engine
1. MIN SFOC of engine At 75 per MCR
2. MCR Load on the engine
3.Turbocharger matching (air –fuel Match) In t/c Matching we have to find optimizing point .It is point at which Air and fuel are perfectly match.
If engine is without VIT then optimizing point matching will be carried out at MCR, If it is with VIT then optimizing point will find anywhere in between 90-100 per ( Present day engines brake point is at 90 per MCR)
Fuel used:- MGO
Turbocharger matching:-
Ø type and Dia. Of Nozzle ring
Ø Temp, pressure, Surging etc to check Efficiency
*** Trial and Error method
T/c matching + VIT = 85% to 100% MCR
Without VIT = 100% MCR
Safeties that should be in place before carrying out shop test 1.Oil mist detector
2.Overspeed trip
3.Crankcase relief valve
4.Bearing wear monitoring
5.LO low pr trip
During the testbed or shoptrial the performance curves of the engine are plotted. The performance curves are the graphs of different parameters on x-axis plotted against engine power or load on the y-axis. These different plotted curves are as follows:
Engine RPM v/s. Load: This curve helps in ascertaining whether main engine is overloaded or not. A higher power generated at a lower RPM indicates an over loaded main engine.
Mean effective pressure v/s. Load: Mean effective pressure is used to calculate horse power hence these two values should co-relate. In case they don’t then there may be some error in calculation or instrumentation. Maximum pressure v/s. Load: This curve helps in knowing the condition of fuel injection equipment, injection timing and the compression in the cylinder etc.
Compression pressure v/s. Load: This curve indicates the condition of the parts maintaining compression like piston, piston rings and exhaust valves.
Scavenge air pressure v/s. Load: It indicates the condition of the Turbocharger and associated equipment.
Exhaust g as temperature in receiver v/s. Load: It indicates the enthalpy of the exhaust g as prior to entry in Turbocharger. This value compared with the value after the Turbocharger gives the temperature drop across the Turbocharger, is an indicator of Turbocharger efficiency.