LPG EGTs

[storm]

After reading a bit on Diesel engines that have had LPG added to them a core topic of concern is EGTs (Exhaust Gas Temperatures). Now I know diesel engines are very carefully designed to run within a certain EGT range (I don't know what the range is and I'm not all that interested either). What I am interested in is LPG EGTs, as in a Petrol engine that has been converted to run LPG. What is the "correct" range of EGTs for LPG? Is there such a thing as an optimum EGT for LPG? If yes what is it?

I suppose this is a performance related question in that the average conversion that is on a car that isn't stressed much wont go melting piston tops but LPG performance and/or race cars, and a quick google shows there are a few around, are subject to much higher stress levels so I'm thinking EGTs would come into play on such a vehicle.

[franz]

LPG has a longer burn duration than gasoline, and if the engine is not optimized for LPG, the combustion can continue when the exhaust valve opens, leading to excessive valve temps and overheated valve seats. Ignition timing advance kits help a little and improve performance in certain RPM ranges. Lower compression ratio engines tend to exacerbate this problem while higher compression engines tend to show improved or lower temps.

There is no target exhaust temp, but ideally, they should be as low as possible. High exhaust temps indicate inefficiency since ideally, all the combustion should be inside of the combustion chamber. In a perfect engine (emphasis on perfect), the exhaust will be at room temp. Since engines operate at around 28% efficiency, a considerable amount of heat is lost through the exhaust.

Choosing an engine configuration is always a compromise. High compression improves efficiency but the engine becomes "touchy", meaning, it must be tweaked to maintain fuel mixtures and timing to prevent damage. Low compression allows sloppy timing and fuel mixtures but is less efficient.

Franz

[Steptoe]

Lower compression ratio engines tend to exacerbate this problem while higher compression engines tend to show improved or lower temps

I found this when I rebuilt to just under 11:1....lean advanced, whatever it will not run hot and towing makes no diffrernce once the thermostat has opened.....except when I hit the high altitudes above snow lines...and even then temps only get to 190 F max

High compression improves efficiency but the engine becomes "touchy", meaning, it must be tweaked to maintain fuel mixtures and timing to prevent damage

interesting comment...yes I do have problems getting leaner mixtures at very low rpms (1050 rpm=30 mph) but get up to 1800 and above nps... till around 4500 WOT but that because limitations of cfm in the carb.
Yes changes in timing are far more sensitive to power and economy with the higher compression..espec economy.
As to damage, when we stripped the engine down a while back after 100K plus, other than worn valve giudes, and they where no more than expected, rescession, wear, pistons, bottom end etc was far more less than would have been expected on a petrol engine...so much so one would say it was an engine that had only done a few thousand miles. only.
I dont know ewhat it would be like if it was duel fuel thu...it had never seen petrol even on intial fire.
I have never used special oils or additives...basically any virgin oil (not re refined) that happens to be on special.
I did use Slick 50 about 10K after break in..a one off.

If a engine was hi compression (high cylinder pressure varies as to cam rpm range) and duel fuel, I wonder if it is the compromise rather than the LPG that results in long term damage????
Or where the installer just increases the intial to give added advance at low rpms, but way over advanced at higher rpms...in effect at highway cruise the pistons are still coming and fires well before max cylinder pressures????

[franz]

Many "tuners" just crank in initial and total timing based on a guess instead of accurate load based timing. All timing should be based on three factors: load, detonation and emissions.

In an engine development facility, an engine is brought up under various load conditions and the timing is increased until there is no further power increase OR detonation is detected. It may not even be audible detonation. The engine may be set at as many as 30 load points with the same number of RPM steps to establish spark timing mapping. This is totally separate from fuel mixture mapping.

Second, ignition timing is advanced until there is an increase in HC+NOx, regardless of power increase.

There are a number of other factors that can change these values: Compression ratio, barometric pressure, piston shape, combustion chamber shape, cylinder head material (cast iron or aluminum) intake air temperature, air to fuel ratio, combustion pressure (which can be changed by camshaft profile), connecting rod length, bore to stroke relationship, spark plug heat range, and fuel type or quality.

Finally, once the engine is running, the total air-fuel mixture and mapping is balanced against each other as long the three factors are followed.

This is why "one timing setting" does not not always fit all engine conditions.

[storm]

Many "tuners" just crank in initial and total timing based on a guess instead of accurate load based timing. All timing should be based on three factors: load, detonation and emissions.

Modern ECUs take care of the first two as long as they are setup properly with MAP or MAF plus Knock Sensors as a minimum with Intake Air Temp Sensor also being a very useful add on. The 3rd has way to many factors to take into account for a simple O2 sensor to be able to deal with. I myself use a Kalmaker unit (Modified Delco to run in Real Time) and it is an easy unit to work with.

As for old school non ECU tuning (optimising) I've never had to do it and doubt whether anyone in my local area would ven ask for it now.

[Steptoe]

As for old school non ECU tuning (optimising) I've never had to do it

Im the other way around..still old school... all our cars, camaro the vintages, even the subaru are all old school.
Set them up..oil change, occassional plugs, tyres battery and forget for the next 10 or 20 yrs.
Modern cars always gave some bloody sensor or CV joint , cam belt, injector etc needs doing.

[storm]

I suppose if I could get hold of a good Sun Distributor machine I'd consider doing old school.

While I agree in principal that new technology can cause issues with sensors etc. I like the simplicity of adjusting the Delco ECU. Things like having knock sensors in place gives an added level of protection in the odd instance of bad fuel.

The reason I asked the initial question, getting back on topic, is that one day I would like to get my old girl on a dyno and see what effects different tunes have on things like EGT as it is something I have never really worked on.

[Steptoe]

I suppose if I could get hold of a good Sun Distributor machine I'd consider doing old school.

yep got one of those.
I have found chassis dynos get you close in the ball park, but out on the road always need a bit more fine tuning.
not much....dynos are very dependant on the technicians skills, both setting up the dyno and tuning.
Its like taking a 1st gen camaro to get a full wheel alignment...goes ok after but they have screwed it up...keep adding shims and stuff the overall squareness with the rear , and pull the steering wheel off to straighten it...it sits only one way on the splines and they dont know that one sets the steering wheel THEN sets the tie rod ends

[storm]

I suppose if I could get hold of a good Sun Distributor machine I'd consider doing old school.

yep got one of those.
I have found chassis dynos get you close in the ball park, but out on the road always need a bit more fine tuning.
not much....dynos are very dependant on the technicians skills, both setting up the dyno and tuning.

Dynos don't really approximate road conditions such as wind resistance and that is just one example why you need a good operator.

Its like taking a 1st gen camaro to get a full wheel alignment...goes ok after but they have screwed it up...keep adding shims and stuff the overall squareness with the rear , and pull the steering wheel off to straighten it...it sits only one way on the splines and they dont know that one sets the steering wheel THEN sets the tie rod ends

I know what you mean. However, that all depends on how straight and original the steering was in the first place. Even a minor accident can throw stuff out. My old TA was a shocker to set up cause of damage done in America by a previous owner and the screwed up RHD conversion not taking that into account.

My last job was in a tyre/wheel alignment shop and we used to get all types of not so common anymore cars. 1960s VW Kombi for a wheel alignment anyone? How about the old R,S or even just a normal 1960s/70s Valiant for a Wheel alignment? Living in a medium sized (read 50000 population) rural regional centre meant no one else knew what to do so on quite a few occasions I had some Googling to do.

[400HPONGAS]

Mr Storm , Ill bet you that my old school fumigated Holden V8 355 stroker will eat any of your Closed loop systems or SQVI especially on STRAIGHT LPG .
As Franz has said , you need to understand the whole range of parameters that make the end result .As for EGT's , again this depends on the Head design m theb cam events and your entire induction systems , Since I Build engines that run 110 % VE by controlling/porting the heads/valve s combo t. If you look back through previous threads youll see I run Twin wideband Digital readouts and all 8 EGT readouts , Since I run a static comp of 12:1 . (but a big solid cam as well)them I would expect a EGT of ov600=620C under full load with a light load cruise of 450 C and a Idle of 300C . If you dont Burn fuel then you dont make power , so 450Hp requires a certain amount fuel and will give a certain EGT , as does 300Hp . as does 200HP

[storm]

Apart from the temp range, thanks for that info it is what I was after , much of the rest of your post is 1st year TAFE material

As Franz has said , you need to understand the whole range of parameters that make the end result .

I understand what Franz said, I asked the question because I didn't know what range EGTs LPG produced and what was a safe range. Being a dry fuel with very different burn characteristics to Petrol it has to be different to a certain extent.

Mr Storm , Ill bet you that my old school fumigated Holden V8 355 stroker will eat any of your Closed loop systems or SQVI especially on STRAIGHT LPG .

I'll bet you have no idea what I have done so I am wondering why you headed straight to bragging rights. It is well documented all over the internet what you have done. I wont comment further on this except to say I don't appreciate your condescending attitude.