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In a traditional marine diesel engine its power is produced by hot compressed air igniting fuel which has been sprayed into the cylinder head under very high pressure. A marine diesel engine does not have a carburetor to mix the fuel or spark plugs to ignite the mixture. Instead it uses the pistons to compress the air to 3000 kPa, which causes it to become very hot and the fuel is ignited immediately it is injected into the cylinder.

Some marine diesel engines are fitted with a glow plug in the pre-combustion chamber of each cylinder or a heater plug in the inlet manifold. These can provide additional heat to the combustion air during the starting process.

Diesel marine engines are slower revving and heavier than gasoline engines but they are also more reliable because they do not have to count on external carburetion or that electrical spark for ignition.

Many newer engines employ an electronic fuel injection system where fuel and air are mixed more thoroughly in the pre-combustion chamber before entering the cylinder. This system maximizes fuel and power economy and is also less polluting.

All skippers should understand the basics of marine diesel engine maintenance so let’s start with an explanation of the mechanical cycles.

Most reciprocating piston internal combustion engines work on one of two mechanical cyclesóeither the four-stroke cycle or the two-stroke cycle. These cycles list, in the correct order, the mechanical actions by which the fuel and air gain access to the engine cylinder, the gas pressure – due to combustion – is converted into power and, lastly, the burnt gas is expelled from the engine cylinder.

The Basic Four-Stroke Marine Diesel Engine

From its name, you should understand that there are four strokes in one complete engine cycle. A stroke is the movement of the piston through the full length of the cylinder and, since one such movement causes the crankshaft to rotate half a turn, it follows that there are two crankshaft revolutions in one complete engine cycle.

In the order they occur the four strokes are:

1. Inlet Stroke. With the inlet valve open and the exhaust valve closed, the piston moves from top dead center (TDC) to bottom dead center (BDC), which creates a low-pressure area in the cylinder. Clean, filtered air rushes through the open inlet valve to relieve this low-pressure area, and the cylinder fills with air.

2. Compression stroke. With both valves closed, the piston moves from BDC to TDC, compressing the air. During this stroke the air becomes heated to a temperature sufficiently high to ignite the fuel.

3. Power stroke. At approximately TDC, the fuel is sprayed or injected, into the hot compressed air, where it ignites, burns and expands. Both valves remain closed, and the pressure on the piston crown forces it down the cylinder from TDC to BDC.

4. Exhaust stroke. At approximately BDC the exhaust valve will open and the piston starts to move from BDC to TDC, driving the burnt gas out of the cylinder through the open exhaust valve.

Two-Stroke Diesel Engines

The two-stroke engine uses two piston strokes to complete one power stroke and, therefore, fire twice as often as a four-stroke engine. A two-stroke engine is smaller and simpler with fewer moving parts. A two-stroke engine has the potential to produce twice as much power as a four-stroke engine of the same size, however, because of the extra fitting required in a two-stroke diesel engine, for example blowers and governors, they become more expensive to produce. There has been a move towards four stroke diesel engines of late as they have become smaller and more efficient.

Protecting Your Marine Diesel Engine

The engine is often idled to charge the batteries or cool  the refrigeration but if done repeatedly it will glaze the bores of the engine and cause premature engine failure. Avoid idling your marine engine for periods of longer than ten minutes in a no-load state. If the boat is berthed the engine can be put in gear to create load at idle.

Every boat owner should have some knowledge of basic marine engine maintenance so grab a copy of Marine Diesel Engine Maintenance For Beginners and keep yourself and your family safe while boating.

kenhay Boats & Boating, Cruise Travel, Cruising Burnt Gas, Carburetion, Combustion Air, Combustion Chamber, Diesel Engine, Diesel Engine Maintenance, Diesel Marine Engines, Electronic Fuel Injection, Electronic Fuel Injection System, Engine Cylinder, Fuel Injection System, Gasoline Engines, Glow Plug, Inlet Manifold, Internal Combustion Engines, marine diesel engine, marine diesel engine maintenance, marine diesel engine servicing, marine diesel engines, Mechanical Actions, Power Economy, reciprocating piston internal combustion engine, servicing a marine diesel engine, Stroke Cycle

The International Recreational Crew Certificate is divided into 6 modules, module 2 gets us under way and you will be learn about safety on board a boat and the use of the life raft and first aid kit, fire extinguishers, flares, life jackets and safety harnesses. What clothing and footwear is suitable for the varying conditions met while sailing. Seasickness and it’s symptoms, cause and prevention. How various equipment works including: battery selector switch, bilge pumps, cabin lights, cooker & butane/propane gas, heads and water pumps together with general housekeeping rules. You will learn a very basic theory of how a diesel engine works and maintenance procedures such as checking the level of the oil, changing the oil, changing filters, ensuring the flow of cooling water to the engine and how to change impellors. You will be taught how to keep a good and effective lookout, which should be maintained at all times, while under way. You will take a look at basic navigation, course plotting, nautical charts, safe passage conditions, tides and currents and weather forecasts.

On the practical side, module 3, you will learn how to coil a line and secure it to a cleat, tie a number of knots and use the winches. You will learn how to secure the boat for sea and then how to leave a berth, once under way you will undertake the duties of a lookout, learn how to hoist and set the sails and while helming the boat go through tack and gybe routines. You will anchor the boat and go through man overboard recovery drill.

Module 4 is theoretical and you will look at the International Regulations for Collision Avoidance or the “rules of the road”. Specifically looking at lights, shapes, and sound signals. You will look at some more sail handling techniques, there is more work with charts and compass and to conclude you will take a look at marine customs, etiquette and manners.

The next practical module includes safety checks and look at the through hull fittings, engine warning lights and alarms and the emergency fuel cut off. You will learn deck seamanship with more docking and mooring routines. More sail work, bending on, hoisting, lowering, reefing mainsails, handling sheets, lines, halyards, outhauls and sail trim. You will learn more skills at the helm, tacking, gybing, sailing a triangular course, sailing a compass course and heaving to.

Module 6 looks at both theory and practise of Dinghy/Tender handling. You will learn the different types of tenders, engines, spares and maintenance and safety equipment. On the practical side you will learn to row, how to move under power, launch and recover and transfer to and from the dinghy to the boat or dock.

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kenhay Boats & Boating, Cruise Travel, Cruising Bilge Pumps, Boating, Butane Propane, Collision Avoidance, courses, Diesel Engine, Diesel Engine Works, First Aid Kit, gybe, Housekeeping Rules, international yachtmaster training, iyt, Life Raft, marine, Navigation Course, Propane Gas, Safety Checks, Safety Harnesses, Sailing, Sailing Courses, schools, Seasickness, Sound Signals, Tides And Currents, Water Pumps, Weather Forecasts