Diesel ICE with EGR injection timing change

[The Chase]

Hello,

I'm currently doing research into the various effects of exhaust gas recirculation for my dissertation at university, the engine being tested on is a naturally aspirated 4 stroke diesel Ford straight 4 (probably out of a transit or something of the sort). Last week I recorded cylinder head pressures of the engine under the effects of EGR and without and noticed something very odd that I can't seem to explain. When I plotted the pressure data into Matlab I noticed on ALL of my data that the injectors seemed to fire later on in the engine cycle while under the effects of EGR. This may be explainable if the engine was controlled by an ECU but the engine in question has mechanical injection! The only explanation I can think of is faulty measuring equipment, but it seems odd that the same 'faulty readings' have happened over and over again! I have attatched a sample of one of my Matlab graphs which shows the problem at hand, any help on this matter would be greatly appreciated!

http://s897.photobucket.com/albums/ac171/mcchase/Physics/

 

[jack action]

I would say that it is due to the oxygen-poor intake charge. For the combustion to start, you need fuel and oxygen. But because, with EGR, fuel droplets have less chance of meeting an oxygen atom, you need to inject more fuel before the combustion actually starts. Just a guess.

 

[HowlerMonkey]

The Nissan LD28 diesel changes injection timing depending on egr operation.

It's part of the engine management scheme.

It's possible this ford engine does the same.

Best thing I can recommend is to learn how they go about managing egr on that engine from the manuals.

 

[The Chase]

Thanks for the replies guys,

@ Jack: I was thinking slower combustion may be a possible answer as EGR has an overall cooling effect on the cylinder head, your theory of poor oxygen content is another idea I haven't though of - thanks! However if you look at the graph i have attached you will notice the point at which injection occurs (just as it temporarily looses pressure due to cool diesel charge) occurs slightly later, so in this regard poor oxygen content shouldn't make an effect up until this point.

@ Howler: I've done a very quick search on the L28 diesel and I assume it also has mechanical injection as there is a timing pulley from what I can see, yet you mention engine management? As I stated before the Ford diesel being tested on has no ECU, it's mechanical injection and isn't variable. I'm trying to get us much information on the engine as possible, hopefully I'll get to the end of this one!

 

[HowlerMonkey]

"Engine management" encompasses diaphragms, distributor weights, and other mechanical devices.

Is it a bosch distributor type injection pump or an inline pump?

 

[The Chase]

Sorry Howler, I've never heard of engine management being used in that context here in the UK! In answer to your question it's an in-line pump, direct injection - I haven't got access to the testing lab until tomorrow but I intend to grab the injector model name and a few photos etc. If you would be so kind though, in the mean time could you give me a brief run-down on how this Nissan system worked? Maybe then I could see if this Ford engine works on a similar method. Thanks again!

 

[brewnog]

Please label your axes. Your pumping curve should be centred around TDC firing.

If this is cylinder pressure curve, you can't conclude much about injection timing because the ignition delay is not necessarily fixed. If you want to look at injection timing, measure injection timing.

What are the running conditions for this back-to-back test? There are several features within an automotive in-line pump which can vary timing so don't think that it's fixed just because it's mechanical!

Do you have needle lift or line pressure traces? If your test conditions are truly identical, I suspect your EGR is doing its job, acting as a dilutant and increasing pre combustion specific heat capacity, and increasing ignition delay.

 

[HowlerMonkey]

Here's a couple of pics from the net but I can photocopy the 10 pages in the factory service manual that describes all the operating parameters.

I'll do it later today.

 

[HowlerMonkey]

The throttle plate is there to create a larger pressure differential between the intake and the exhaust when in use.

 

[The Chase]

Thats some excellent stuff, thank you so much for taking the time to upload those. It seems clear to me after closer inspection to the engine that its likely the mechanical pump is variable which explians my results dilemmal, thanks again to everyone who gave me some direction on this one.