A Containership experienced loss of propulsion 56 miles away from ECA zone. It was reported that main engine unit #3 fuel pump seized when changing over from HFO to LSMGO. The vessel had a spare fuel pump element where the ship staffs replaced the old pump element with the new one. The vessel resumed passage and no more problems were observed.
Fuel Changeover – a Different Ball Game:
There can be difficulties when switching from one fuel to another due to low load operations and leaking pumps caused by low fuel viscosity. This is because distillate fuels can ‘gas up’ at a too high temperatures causing vapour locking and fuel starvation. Low viscosity fuels will flow through fine clearances previously ‘sealed’ by higher viscosity fuel resulting in fuel leakage. Distillates do not require heating like HFO. If the distillate fuel temperature rises higher, the viscosity reduces deeply down to a point at which the systems function incorrectly. Most engine makers recommend maintaining viscosity at injection not less than 2 cSt.
During a fuel changeover process, the heavy fuel oil which is usually at a higher temperature (around 130 degree Celsius to maintain injection viscosity) will gradually be cooled to a safe temperature where the distillate fuel does not ‘gas up’.
The cool down process should adhere to a thumb rule to maintain a temperature gradient (drop) of not more than two degree Celsius per minute during the changeover process. The engine speed/load has to be altered to meet the above thumb rule. Failure to maintain the above thumb rule or to bring the temperature of HFO sufficiently down in order to avoid ‘gas up’ of distillates could possibly result in seizure of fuel pump or fuel system components (or) loss of power/propulsion.
Please note: We have seen that if a vessel changes over from HFO, when MGO is introduced into the fuel system it may act like a solvent, releasing any asphaltenes (sludge) which then collect in the fuel filters/strainers and clog them which could result in a blackout.
Key Factors to Consider:
The most important issues to consider when running on low sulphur distillate fuel are:
1. Viscosity of the fuel – at engine inlet
2. Lubricating oil choice
3. Lubricity of the fuel
4. Change-over procedures to and from residual fuel
Fuel pumps are designed for a minimum viscosity and fuel anti-wear performance. When the viscosity of the fuel in the pump is too low, hydrodynamic lubrication of the pump can be inadequate, causing wear and scuffing.
A decrease in fuel viscosity may cause an increase in fuel leakage between the pump plunger and barrel. The leakage can lead to hot start and low fuel setting start difficulties, especially in worn fuel pumps. It is advisable to make distillate hot start checks at regular intervals so that the limits of operating conditions for a particular engine are determined. Low viscosity fuels can also lead to the engine not delivering the fully designed power output as the design amount of fuel is not delivered by the pump. This has led most 2- and 4-stroke engine builders to request a minimum viscosity of the fuel before the fuel injection pump of about 2.0 mm²/s (cSt).
In the next technical write-up we will cover in detail on the major factors that needs to be addressed in order to execute a flawless fuel switching.
Did you subscribe for our daily newsletter?
It’s Free! Click here to Subscribe!
Daihatsu 3DK20 engine. Fuel pump rack, plunger getting stuck on HFO. These engines using LSMOG for ECA and for start / stop operation. This stuck occurred even on NEW PLUNGER & BARREL.
What could be the reason and how to solve this problem
Kindly help us.
Thanks
Rangan Guha
Chief Engineer
Brilliant write up! Thank you.
This is to share with you our research / discussion in addressing similar challenges of ship managers during the process of changing over from HFO to LSMGO.
The issue of “Viscosity” has been sufficiently covered by you in the above write up.
So, I take this opportunity to touch on “Lubricity”, which is a matter of real concern for LSMGO along with Compatibility; High TAN; & Thermal Stability:
1 HFO & distillate fuels (1.50%S) have a naturally existing lubricating components / characteristics, which is absent in LSMGO and this is one of the main culprits that result in pumping system failure (particularly plunger – barrel in ICE).
2 The assumption that “Low viscosity of fuel (eg LSMGO, ULSFO) results in poor lubricating oil film in plunger – barrel” is probably wrong. Viscosity and Lubricity are two different things and it is not the “Viscosity” that has been creating the pump lubrication problem! However, a minimum viscosity of 2cStk is strongly recommended at the pump inlet to ensure right amount of fuel delivery for designed power output from the engine.
3 Lubricating characteristics of a fuel oil (in this case LSMGO) is rather the result of the “Refining Process” from which it has been produced. The trace amount of polar compounds of Nitrogen & Oxygen are the most critical components that provide “Lubricating characteristics”. These critical compounds are stripped out of LSFO / ULSFO during the severe Hydrotreating process that remove sulfur!
(Reference: Lewis, Ralph; Myth & Reality – LSMGO)
4 So, operating engineers need to understand this fact that by increasing fuel oil viscosity (eg by lowering temperature) shall not provide desired lubricating oil film!
Dear Mr. Ray,
Thank you for the comments. In the above write-up, we have covered mostly on Viscosity and other factors including but not limited to Lubricity will be covered in the future. I completely agree to one important point that Viscosity and Lubricity are two different aspects. We will cover this aspect soon in one of our upcoming technical write-ups. In the mean-time, we request you to post your blogs, technical write-ups or any advice to other Ship Managers, case studies etc. Either you can mail to us or we can publish under your name. Thanks for your above brilliant contribution and detailed comment.
Thank you for your kind words and comments.
You have been doing a brilliant job through your online MFAME, which I strongly believe should benefit all ship managers provided they pay attention to some of the excellent technical details stated in pithy statements by your editorial team.
I shall email to you as and when we come across any relevant item with educational / technical significance for your perusal and posting on MFAME.
The rate at which barrel and plunger cooled/ heated while changing over is not same. The barrel heated/cooled relatively faster than plunger. The plunger is hotter than the fuel and barrel temperature while changing over from hot residual fuel to cold lighter fuel. A quicker changing over to save distillate fuel could lead to a quicker cooling of barrel causing reduced plunger / barrel clearance. Hotter plunger could instantly evaporate the Penetrated lighter fuel leaving contact surface dry. Metal to metal contact will heat up the surface, leading to scuffing and seizure.
A few minutes of warning could be noticed by fluctuating unit exhaust temperature. The seizure is not instantaneous. Plunger stick on / off few times before seizing it for final. If it can be detected immediately, changing back to hot residual fuel will help. The newest plunger with lower clearance will be the first victim.
Never try to economise on the distillate fuel during changing over. Ensure sufficient time is allocated for this critical process much ahead of arrival ECA
Mr.Ali, you are absolutely spot on. Many Chief Engineers rush to save some distillates and end up in such trouble. You are welcome to share your views/opinions and experience with the maritime world. Thanks for your comments.