Okay i have had a request to tell you lot a bit more about what i work with as it apeals to some of the petrol heads out there.

it is assumed by many the biggest piston engines you are liable to ever get are truck engines well very wrong on this acount i sail on engines that are huge but what i work with are by no means the biggest you get those on containerships the biggest i know of is a sulzer (maker) 12RTA96C which is a 12 cylinder engine of the RTA model with a bore of 960mm and is optimised for Container ship use which produces about 98,000Bhp at 80rpm.

they compression ignition engines where the heat of compression of air heats fuel to the point of buring basically and they operate of a 2 stroke cycle instead of the four stroke cycle most cars operate on.

Four stroke being 2 rotations of the crank for each power stroke or SUCK SQUEEZE BANG BLOW as it is known

2 strokes fit it all into 1 rotation of the crank by getting rid of the exhaust gas and bringing in the fresh air at the same time called scavenging to me

To achieve this a 2 stroke engine must be either supercharged of turbo charged At this point some of you will say rubbish your lawn mower is 2 stroke and not supercharger well i am afraid it is it uses under piston charging where the mixture is compressed below the piston and then realeased into the ombustion chamber throught the inlet ports.

The engines i work on are turbo charger with two turbos which both stand about 6 foot tall including thier mounts.

I also mentioned previously exhaust valves yet another thing not found in your lawnmower/motorbike/outboard/whatever. A 2 stroke that uses ports in the side of the liner to control exhaust and inlet is termed a loop scavenged engine as the charge comes in and does a loop round the combustion chamber (leads to mixing of exhaust and frsh air not good) the two strokes i work with have the normal inlet ports at the bottom of the liner timed by the piston but the exhust port is controlled by a valve in the clyiner head so the exhaust and air are flowing in one direction called uniflow scavenging. It looks just like a normal exhaust valve out of a car but needs two people to lift it and is about five foot tall.

We open this massive valve hydraulically using a pump off the camshaft (rotates at engine speed unlike 4 stroke where it is half engine speed) and then we close it using compressed air springs which is now almost standard in formula 1 engines.

The engines run at slow speeds due to two main factors a piston on its own wieghs about 2.5 tonnes and a conrod is about the same these don't take to kindly to high speeds and propellors are more effiecent when they are big and slow. So the last ship i was on max Rpm was 64 flat out pedal to the metal27,000bhp from a sulzer 7RTA84M

So another thing that you might wander at is how do you start this this thing with about 80tons of rotating parts.
starter motors are a complete non starter so what is done is that we introduce compressed air into the clyinders in sequence.

We have two big bottle with air stored at 30bar which is then pipe into the clyinders in sequence. But it is a compression engine has a compression pressure of 100bar how does it over come this? what is done is air is introduced through most of the stroke so since one crank will be a about 90degrees when another is at top centre we get by it by the increased leverage.

One little thing to think over is we have a peak pressure of 130bar when running in the clyinders which are 840mm in diameter work out the firing load for yourself.

things are also starting to get intresting in marine engines as the sulzer company have just built the flex engine which is based on the RTA but has no camshaft everything is controlled by a computer which opens and closes valves and also controls fuel injection which is pretty damn clever.

so anymore questions will be happily answered and i shall try and dig up some pictures to post or i might be brave and attempt a website to use up me free 50meg with my ISP