For those who enjoy a life on the sea, fire should be no stranger. Marine diesel engines and vessels are powerful and complicated machines that deal with hazardous and combustible materials, carrying fuels and oils that could become ticking time bombs if the proper precautions are not taken. Even so, fuel and oil tanks are not the only common sources of fires and explosions aboard vessels, but also the machinery itself – such as engines and generators. Much like the scavenge fires that we discussed in a previous article, an expert sailor aboard any type of vessel worth his sea salt must be prepared to prevent such events and to know how to deal with them if they do indeed occur. However, scavenge fires are not the only fire-related danger to sailors of marine diesel vessels. Marine diesel fires can also occur during a crankcase explosion, one of the worst types of diesel mechanical disasters.
For any fire or explosion to occur, three basics elements must be present – heat or energy, oxygen, and a fuel source. Obviously, as they are powered by combustion, the crankcases of marine diesel engines contain all three, potentially making them ticking time bombs if not properly operated & maintained. Fortunately, under the operating circumstances of a healthy marine diesel engine, specific factors keep these explosions from occurring. While oxygen is indeed present in the crankcase, the concentration oil and air is too weak and the lubricating oils also inside the crankcase are in droplets too large to burn at the speed required for an explosion. However, if a fault were to happen with the moving mechanical parts of the crankshaft, and too much friction were to be generated, it can create an area of heat inside in the crankcase what is referred to as a “hot spot”.
If the friction caused by this malfunction produces a hot spot with enough heat, about 200°C, the lubricating oil that reaches this hot spot will vapourize, then circulate into the cooler section of the crankcase where it rapidly cools and condenses into an oily mist. Once the temperatures in the hot spot reach about 850°C, then this oily mist will ignite, causing the crankcase to explode from the inside. The intensity and severity of these explosions can be subjective, varying from causing repairable engine damage to catastrophic fires, complete devastation of a vessel, and multiple deaths – the extent of the damage caused by these events is largely dependent on the amount of oily mist that has accumulated in the crankshaft.
Regardless of what toll an individual crankcase explosion may take on your vessel, it is definitely not something you want to have occur in any case. Fortunately, there ways to check your marine diesel engine for early warning signs and prevent a crankcase explosion from happening to you. When running your engine, a sudden increase of exhaust temperature, irregular running of or increased load on the engine, irregular noises from the engine, and a noticeable smell of the oily mist in the heat spot are all pre-explosion signs that if detected early may save your engine, you vessel, and your life. But of course, the best first step is to take preventative measures instead of dealing with the consequences after something occurs. Having regular maintenance performed on your marine diesel engine is extremely important, but some specific measures you can take to prevent your engine from experiencing a crankcase explosion are providing proper lubrication to the reciprocating parts, not overloading the engine, and periodically testing your engine’s pressure relief valves.
