Eco-Friendly, But . . .
Back in the early 1990s when the automobile industry shifted to low-sulphur diesel, disaster struck. About 65million fuel pumps failed after running for only 50,000-10,000km. Assuming an average speed of 50km/hr, these engines ran only for 100-200 hours before failure. For marine engines, this is not even too short a duration.
Environment is the mother resource providing us with anything and everything we need to survive, thrive, and prosper. And we all have a sacred commitment towards Mother Nature.
Even before January 1, 2015 when the 0.1% (by mass) cap on fuel sulphur came into being in Emission Control Areas (ECAs), the same cap applied to ships berthed at European Union (EU) ports and within 24 nautical miles of the Californian coast. Coastal U.S. and the Mediterranean will soon follow suit.
Low-sulphur fuels have low lubricity causing seizures, fuel pump failures, and problems at low and high loads that can turn lethal and endanger the safety of vessels. These fuels promote cylinder liner lacquering, although definitive evidence is awaited. Moreover, low-sulphur fuels are weak in fighting off the effects of ethanol and water contamination.
Challenges & Remedies
Combustion headaches in diesel engines have varied over time. While corrosion and carbon deposits were the main challenges before 1985, bore polishing and liner lacquering emerged as the principal troublemakers in 1985-92. Then in 1992-95, piston undercrown deposits and bore polishing assumed larger proportions.
Sulphur does not improve a fuel’s lubricity. However, hydro-processing used to lower sulphur content in fuels ends up eliminating naturally occurring polar elements that provide lubricity to fuels. Certain aromatics, compounds with trace oxygen and nitrogen, and high-molecular-weight hydrocarbons provide lubricity.
Revised in July 2010, ISO 8217 Specification for Marine Fuel mandates lubricity testing of distillate fuels with sulphur content below 550ppm (0.05%). Lubricity is the inherent ability of a fluid to provide lubrication between contacting metal surfaces. It does not depend solely on viscosity and can be:
- Hydrodynamic Lubrication increases with increasing viscosity. It depends on the oil film created between moving surfaces. Oil films lose thickness at higher temperatures. Very thin oil films cause:
- Seizures due to fuel leakages across nozzle needle valve and fuel pump plunger
- Starting Difficulties
- Safety Issues due to Problems at Low and High Loads
- Boundary Lubrication is independent of viscosity. Low boundary lubrication causes excessive wear in the microscopic gap between the plunger and the body of the fuel pump hastening its failure
Common rail fuel pumps and individual cylinder reciprocating fuel pumps are most prone to such failures that are extremely unsafe, expensive, and time-consuming
Another major issue with low-sulphur fuels is their weakness against ethanol and water contamination. Sulphur in high-sulphur fuel used to act as a biocide and check these effects. That is no longer the case.
Switch Loading is a common practice in the road tanker segment. Under this, the same tanker is used to transport different types of fuel thereby causing cross contamination or mixing of fuels.
This is precisely how ethanol from ethanol-blended gasoline found its way into low-sulphur diesel tanks. Such cross contamination corroded diesel fuel tanks, associated pipes, and fuel delivery pumps. Ethanol boosts a fuel’s acidity and catalyses corrosive damage.
High sulphur content in fuels also boosts acidity, but after combustion when it produces sulphuric acid. This acid promotes engine wear and corrosion while cutting relative engine life and lowering the efficiency of exhaust after-treatment systems. Lubricants contain alkali additives to neutralize acids produced by combustion.
Incomplete fuel combustion produces more soot that absorbs more sulphuric acid leaving more sulphuric acid in the lubricating oil. Alkali additives in lubricants neutralize acids. A cylinder lubricant’s neutralization efficiency depends on its alkaline content and the speed at which its neutralization temperature rises. The faster, the better.
Presence of water in diesel tanks aids the growth of mold, fungi, and bacteria. These organisms use diesel as food and their secretions lower fuel quality leading to clogged filters and equipment failure. Acetobacter for example has affinity for ethanol and produces acetic acid that corrodes tanks.
Switch loading and cross contamination are road tanker segment realities we cannot wish away. We can however institute:
- Regular Biocide Treatment of Tanks checks corrosion. Use biocides that provide long-term microbe-control. This ensures the biocide kills microbes attached to upper walls of the fuel tank when additional fuel is added later
- Monthly Water Paste Test to detect water. You can either pump out detected water or use fuel treatments that arrest water while allowing pure fuel to pass
Prevention, as is usually the case, is many times more cost effective and hassle free as compared to curative measures. With the shipping world inching closer to greener fuels and products, preventive measures are the order of the day.
Want to keep updated with the latest in the marine industry? Visit our blog. For top class ship repair, marine fabrication, and large scale custom metal fabrication, contact us at Kemplon Engineering.
Marine Engine after Piston Seizure & Crankcase Explosion (Source: http://www.marinediesels.info/Horror%20Stories/crankcase_explosion_3.htm)