Injection timing

[Diesel Dave]

Given that most small single cylinder stationary diesel engines have fixed timing I did a little digging on the effects this might have.

My experience is with my 6LD400 powered Enfield so this was the test bed.

Tests were carried out by running full bore up a local incline 3 times and noting the speed at a set point.

With the std 18:1 compression piston and UK pump DERV rated at 51 Cetane advancing the timing by one shim did nothing to improve performance (1 shim = 1.7 degrees of advance).

Removing one shim made a noted improvement although 2 shims less made results revert to the original level.

This equates to about 24 degrees of advance, idle was improved with less knock and the motor was easier to start when cold.

Moving to a higher compression piston of 20:1 from the B1 variant of the motor (this is used on the generator version) has seen the return of a harsh knock at idle and some drop off at the upper end of the rev range.

More experiments are needed in regards to changing the timing to suit the new higher compression ratio.

Now why would this be?

My thinking goes along these lines:

The high cetane value of the uk pump fuel as compared to the 'red diesel' that would usually be used in these engines results in a shorter ignition delay after injection. Effectively advancing the ignition beyond its best timing position.

Switching to a higher compression should increase power and effeciency however one of the side effects is to accelerate the burn speed and shorten ignition delay due to the higher temperatures of the compressed air. This is noted by the results of the tests where the increased idle knock and slightly lower top end power was noted. This should be correctable by retarding the injection timing by a few degrees.

This will be the next stage of analysis but I would be happy to hear from any knowledgeable sources on this matter.

Regards to all

Dave

[andrewaust]

Your analysis is pretty much spot on, increase compression, increase heat which in turn quickens the burn and it's actually more of an explosion of sorts resulting in a sudden pressure wave causing knock, pilot injection is one way around it, not achievable on our diesels. The old 16:1 Engines didn't knock as hard but also gave poor combustion when cold, still remember the slag coming from them diesel loco engines, also old buses and trucks which ran low compression. Surprisingly the old Perkin's 6-354 gave brilliant fuel economy, even though they were fairly low on compression, but white smoke would clear if run hard, if set up right very little black smoke would be seen until someone played with the injection pump

Knocking the timing down bit by bit can help.



A

[Diesel Dave]

Experiment 2 completed with the retard notch injector pump, this is the version used on AGR versions and for the gen set versions also, below half rack it retards the injection.

I'm actually very impressed with the results, much more power at top end, test run hill RPM increased from 2500 to 3000 so that's from 38 to 45mph, quite an impressive improvement.

Some adjustment is needed as it's over injecting and blowing a bit of black smoke which makes the throttle very sensitive.

It also likes to rev a lot so runs through 3600 like its not set as a limit and did hit 4000 at one point so again more regulator adjustments are needed.

Onwards and upwards.

Dave.

[Diesel Dave]

With the weather turning colder in the UK, I've hit a problem - can't start the bugger in the morning.

It was foggy and just a few degrees above freezing but after 20 minutes trying to kick start I gave up and put the hot air gun on the cylinder.

Not a good day as I also managed to pick up a wood screw in the rear tyre too.

I might try the low compression piston with the dual stage injector and see how that measures up.

[Sphere]

Interesting read. With headwind 3-5Bft. I cant manage to go above 65-70km/h. Actually it would seem the speed in 3rd and 4th gear is identical. Too slow, even for secondary roads. Oh well, maybe my engine will loosen up some still.

[skoleskibe]

How does that retarding below half rack work ?
I'm using a yanmar L100 engine, and would love to find a way to have some kind of injection timing regulation according to rews and load.

[Diesel Dave]

There is an additional notch in the injector pump plunger.

If you wanted to add this I suppose you would just need to replace the injector pump with the AGR type.

[alexanderfoti]

I dont think there is an AGR type pump available for the yanmars?