How it’s made: diesel injectors

Apr 18, 2017 Technology

A well-running diesel sounds like music to the ears of any skipper, writes Matt Vance. Keeping the tempo constant is the humble injector.

If you listen to the sound of a marine diesel engine on a long night watch you will hear all sorts of music. In the beat of the engine you may hear a male voice choir, a distant nightclub or even a pipe band if you have been at it long enough.

The core of this curious illusion is that a diesel goes ‘bang, wallop, wallop,’ this is the only real bit in the
equation – the tired mind does the rest and you end up with strange music. The key ingredients in all this beautiful music are the diesel injectors.

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They lie on the junction between the biblical-sounding low and the high-pressure sides of the diesel engine fuel system. The injectors are where these fundamental forces of the cosmos meet and battle; and for that reason they are one of the more critical parts of a diesel engine.

Your local grease monkey will always have his eye on the injectors come service time and will develop a Gypsy tea-leaf reader’s fascination for interpreting their health in your exhaust smoke.

The average diesel injector is not a complicated piece of machinery, it usually consists of a needle valve, spring system and casing that can be threaded into the cylinder head. It is, however, a meticulously machined and highly-sensitive part of your engine.

The best way to see it all happen is to watch the YouTube clip from German manufacturer of diesel injectors Monark Automotive – click here.
The clip covers the entire manufacturing process and, given its entertainment value, it’s surprisingly that it’s the only show that deals with the production of diesel injectors on the entire world wide web.

If you follow the clip it goes something like this:
• Raw steel is placed in sophisticated CNC turning machines which look like large computer-controlled lathes with headache-inducing precision. This is accompanied by disturbing psychedelic 70s music
• The resulting parts are tested for fit and marked with codes identifying their origin accompanied by news headline drum and bass
• Internal machining of the base is again carried out by CNC turning machines, accompanied by some down-beat hip-hop
• The parts are then taken to a hardening shop and baked at 600°C and subjected to the sounds of heavy metal which is quickly toned down to some Greek mandolin-inspired drum and bass
• The parts are then CNC ground to exceptionally minute tolerances
• The pins are prepared for having their nozzle patterns eroded into their tips by robotic drills with some country/hip-hop fusion to help it along; this really makes your eyes water
• The resulting components are polished by yet another robot to  a nad’s whisker of tolerance and to the sounds of Barry White
• The components are checked again under a microscope for their final quality assurance and the whole lot is capped off with some euro electronica.

While their music choices are erratic the finished product is not.

The main purpose of the injector is to deliver fuel to the cylinders. It is how that fuel is delivered that makes the difference in engine performance, emissions and noise characteristics.

Unlike its petrol-fuelled, spark-ignited engine counterpart, the diesel fuel injection system delivers fuel under extremely high injection pressures, which means only a well-machined precision product will handle the treatment.

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While the injection timing must be well-controlled to deliver an accurately-metered amount of fuel at the right time, it is the head of the injector that atomises the fuel particles that is critical. Small droplets ensure that all the fuel has a chance to vaporise and participate in the combustion process.

Any remaining diesel droplets will burn poorly and will be expelled in the exhaust and into the noses of grease monkeys who are always suspicious of injectors. Too much or too little diesel being atomised and they will smell it and charge you a bomb to fix it.

On those long night watches it is still ‘bang-wallop-wallop’ for hours on end. A mighty melodic miracle spurred on by the humble injector keeping the competing forces of high and low pressure apart and driving both sailors and injector manufacturers to bad taste in music.