Hypermilling on LPG
 

Hello everybody,

I'm new here, but I've been reading with interest for a while the threads on the forum.
I own a Hyundai Accent with a 1.3 SOHC engine, which has a pretty good mpg rating, but I always try to improve it. My personal best was a 51 mpg and the official rating is 45 mpg for highway driving.
The fact that I live in Romania, makes hypermilling a very different thing from what I've read here. Usually extra-urban driving implies a legal speed limit of about 55 mph and lots and lots of villages and curvy roads to drive through.
It has been a month now since I installed on my car a lpg system. This gives me a financial advantage, because lpg is about 60% the price of petrol. Also lpg burns cleaner.
All is good, except the fact that when switching on lpg, the car has worse mpg.
It is not a big difference ( about 10% ), but I don't like it. I think that this is also because the car feels lazy when running on lpg, but I did manage to get the difference in mpg to a 3-5% compared to gasoline.
Is there any special advice for driving a lpg car ?
Are the usual hypermilling techniques different for this kind of fuel ?

I#d be interesetd in this too- an LPG conversion will be on the horizon shortly for the 3218iS, aS I cant ignore the £0.70/litre cost as opposed to the £1.34 a litre of unleaded

I drove a dual fuel (Petrol / LPG) van for years and unfortunately, less power and higher fuel consumption are normal for this type of conversion. Lower fuel costs still make it worthwhile though.

I only used engine on coasting with mine due to it's auto gearbox. However, engine off coasting may have been a problem anyway because of the delay in starting with the setup I had.
Mine would start straight away on petrol, but the LPG only turned on after engine vacuum was detected, so the engine needed to be cranked longer.

If you're lucky, your more modern system may not have this issue?

Pete.

Gasoline has about 128,000 BTU's per gallon, while propane has only 92,000. On the other hand, propane is 110 octane. Propane will get fewer miles per gallon, but could get more miles per BTU if the engine is knock limited.

If the kit is a venturi type, you can have it adjusted, old-school style, by tuning the flow, as on carburetor. You can look for adjustment tips online, I suppose. A lot of taxi drivers around here do it themselves. But it's suggested that you let an expert do this... preferably one with a wideband O2 sensor... as those same taxi drivers blow their engines by tuning too lean.

The problem with LPG is that it runs "drier" and hotter than gasoline... so on cars that rely on gasoline to cool down at high load (by running slightly rich), LPG may cause problems if you tune too close to the edge... tune too lean and the engine simply melts spark plugs. Tune way too lean and you're going to experience an epic meltdown.

---

If it's electronic, they simply need to plug it into a laptop to do the same. Preferably at the shop that installed the unit.

I've some friends who get better economy on LPG after tuning... sometimes as good as or better than on gasoline... but this presupposes that your engine was poorly tuned on gasoline... in one case, one owner experienced a gain in economy because his fuel-injected Toyota van was at 10:1 (air-fuel ratio) at idle! This is far from the ideal 14:1 ratio! On an "economy" car like your Accent, finding an increase or parity in fuel consumption is unlikely... but possible. One Corolla owner sees the exact same economy as on gas.

My LPG unit is retuned to give me the same power as on gasoline (I still make more power on gasoline because we retuned the gasoline system after that with a piggyback controller). Fuel economy is still slightly worse (this is a modified engine on racing cams, can't expect much), but as said... the price difference really makes up for it.

Was your car converted to dedicated propane or is it dual fuel (propane/gasoline)? Propane has different tuning characteristics than gasoline, so dual fuel is typically a compromise.

Is it fuel injected or a gaseous carburetor (mixer)?

The proverbial they say that propane also gets worse mileage because it's entering the engine as a gas (versus a liquid) so it displaces more air.

Wow, thanks for all the replies.

First of all, the lpg system was retrofitted on the car, after I drove it for about 6 years and 90k km. It wouldn`t seem that much for 6 years, but the commute here is very short, with daily trips of about 10 to 30 km. The setup for the lpg system is exactly like this:
www .agrom.ro/montaje2/_30.07/hyunday%20accent/index.htm

The engine is an MPI ( not carbureted ), and the lpg system is Tomasetto complying Euro4 standards. This is funny because the car is Euro3 ratted, but I guess that there is no harm done, except for the money in my pocket. The cost of retrofitting the system was about 900$, but there are systems for carbureted cars that can be bought with only 200$.
The lpg system is very simple - the engine starts on gasoline and when the coolant temperature reaches about 30-40 degrees C, the controller automatically switches to lpg.

The initial tune-up of the system was done at the shop, with a OBD assisted computer, and it did show. The car needs a tune-up, since I`ve covered about 4000 km. Initially, the lpg mpg was very close to the gasoline mpg, but still, not the same. This is the area that I want to investigate.

I mean, maybe insulating the engine block would help - synce lpg absorbs a lot of heat when changing state from fluid to gas.

I did try several aero mods also - a partial undertray front and back. But it seems to me that the one in the back is making things worse for the mpg.
I have a vacuum gauge installed and I use it when driving.
I did a full lower grill block: the aerodynamic on highway speed was great - the car felt very stable and the handling was great, but the mpg dropped a little because the engine wouldn`t get enough air to the air box and the cooling fan would kick in very often.
I sealed the seams on the headlights, front doors and trunk lid.

Also I have some more planned.
I wanted to implement a coolant insulated heat battery - like the one in the hybrid cars. But it seems to me that it is not worth the trouble. Instead I want to use wax to store heat - just place about 1 kg of wax on top of the engine manifold and insulate it. This way, it would absorb heat and slowly release it during the cooling period.

Great forum - I love it :)

After 4k, you ought to be checking your filter and your vaporizer... and looking at your plugs for signs of premature wear or poor running.

LPG likes colder spark plugs, so if you haven't changed already, do so. Doesn't seem to do much for economy, but it helps reliability and power.

If your car is distributor type, you can add a little more advance on LPG... we had to do it with a piggyback. But then, my engine doesn't seem to knock even with extreme ignition advance on gasoline. If yours does, better to not take the risk.

I wouldn't muck around with cooling and engine insulation much. LPG does absorb a lot of heat in the state change, but that occurs in the vaporizer, which only helps with the coolant temperature, which is already managed through the thermostat and the radiator fans switching on and off. What you have to be worried about is the temperature inside the combustion chamber, which is hotter because it doesn't get any of the benefits of the cooling from the phase change, gasoline enters the engine as a liquid spray, hence the cooling effect as the heat makes it turn to vapor. LPG enters the engine as vapor already.

This is why LPG tends to burn out spark plugs that aren't "cold" enough.

LPG will only be superior to gasoline overall when the next generation fuel systems with liquid injection come online... (I doubt yours is if it's only $900...) as those will definitely run cooler than gasoline, with attendant benefits in power and possible parity or even superiority in economy... but I have yet to see a system like this on the market... still hoping...

Then again, as we both know... with LPG dirt cheap, it's still a better alternative, as long as your local filling station carries it. ;)

Until now, in 6 years, the car didn`t need any repair or engine tune-up. Everything worked fine - all I did was the regular maintenance ( actually I did the oil change on shorter intervals ), and I drove it easy - without racing or demanding too much from the engine. It`s a cheap car, so I don`t have high expectations from it - I just want it to run and not to ask for money :).
I expected the lpg system to be self-tuning, as the car engine is, especially because it is an expensive model, and it`s installed using the car`s software.

LPG systems in that price range usually self tune via the stock ECU. But that's programmed to maintain an air-fuel ratio that's beneficial for gasoline, not LPG. Still... if you don't want to overcomplicate, I won't go into O2-sensor intercepts...

You still might see a little power gain via timing adjustment, though.

I believe that LPG should have an AFR of ~15.7.

I went today for a tune-up. So the diagnose / calibration software showed that the system and the car are in very good shape and everything is ok.
The guy from the shop said that it might have to do with the plugs. I will change them as soon as I can and see if there is any difference.
Except for that it seems that the only problem with the low FE is the driver ( me ).

Yup. Go one step colder, at least.

The rest will be up to your driving style.

If you want to look at improving performance, check how your vaporizer is connected... sometimes the car's standard thermostat blocks off the coolant bypass route that takes hot coolant to the vaporizer. You'll want to check that out. If you can keep vaporizer temperature as warm as possible, that will improve LPG stability.

The car has 2 coolant circuits. The small one, is connected all the time to the engine block and to the heater core. The large circuit, is opened by the thermostat only when the coolant from the small circuit heats up too much. The vaporizer is connected on the small circuit. So there isn't much room for improvement there.
I do get the impression that a CAI would help. The outside temperature dropped a little these days and the engine seems to be running a little better.
Also, there is a dramatic improvement when I start with the engine already warmed up.
I have to investigate a series of mods to keep the engine warm for a longer time and to make it warm-up faster.

pmiulian,
I have LPG on my car and also have a slight drop with LPG when I run on that.
The difference is around 10% (around 8.0 or so on unleaded and around 9.0 or so on LPG).

One thing to check is the spark plug leads as well as the plugs.
ANY weakness in the ignition side will usually show up as an erratic idle or slight miss with the car at idle.

Welcome to the place as well by the way.

Peter.

Well, I did the computer diagnose and everything seemed fine. The spark plugs are new and the idle is fine.

I think it has to do with the engine temperature also.

Here`s an ideea I had for keeping the engine warm when not running. Since building an automatic grill block is complicated, what if I mounted some engine bay insulation with a trap door ( in the back of the grill ), so that the trap door would be opened/closed by pulling the parking brake ? So when pulling the parking brake, the door would close.
Just an ideea.

Maybe use a bicycle brake cable (or similar) from the trap door to a knob mounted near the bonnet/hood release?
That way you have the option of leaving it open in summer.

Be careful. Some LPG injector systems have electronics that aren't quite as robust as OEM gasoline equipment, so if you let it get too hot, you might fry something (not literally...).

Why not a block heater? Just throwing it out there.

Also, even if the LPG installer has tuned the engine for best economy, it's not tuned for best power. If you can get to a shop with a dynamometer and bring the installer's laptop, they can tune to give you a bit of extra power. Power by itself doesn't make for better economy, but having a little more kick gets you up to cruising speed quicker, which does.

@D.O.G. - I was thinking the same, about using some bicycle parts. Actually I tried making an automatic system - I bought a thermostat which I would use to open the grill block. Unfortunately the thermostat that I bought I meant for 89 degrees C and my coolant has a temp of about 82.
And the summer wouldn't be a problem since the grill block would close only when the engine is stopped.

@Nicky I can't use a block heater, I don't live in a house - I live in a flat, and the parking space is about 100 m away. Also, I don't really like the idea of a block heater - is like cheating :).

After the tune-up I did a refill and the FE for urban driving is about 7.8 l / 100km - that is about 30 mpg. Which is pretty good - it's above the factory rating.

So, things have happened in the last 2 weeks. I got a SG - yeeeeii :)
And it turns out, it is all worth it. I already had a vacuum gauge installed, but the SG showed me that I didn't know how to use / interpret the vacuum gauge.
With a little SG, a lot of P&G and some DWL, it seems that I am going from a 27 mpg city driving, to an unbelievable 38 mpg city driving. Not 100% sure of that, but that's what the SG indicates. I just filled up the lpg tank and I'll have to wait for the next fill-up for the official numbers.
So all of this is city driving - I can't wait to get a chance to test it on the highway.
Great tool this SG - it does open your eyes on stuff that you thought you knew. Also, it's addictive :thumbup:

I did a 950km trip this weekend and I tried P&G on the highway. The car was fully loaded, but the FE was poorer than I expected. So I got 37MPG highway driving, using P&G, compared to the 38 mpg of city driving. This can`t be right. I`m doing something wrong.
I did use a full grill block upper and lower grill. And the speeds for my P&G were usually 40 - 60 mph or 45 - 65 mph.
Maybe I`m not accelerating as I should, or maybe the speed I use is to high.

Did you calibrate the SG first, using a few actual fill-ups ?

You should accelerate rather swiftly at a fairly high engine loading (LOD on the SG), say 75-80 %, using low revs - in the highest gear that the car can handle.
This puts you in the range where engines usually get their best BSFC, i.e. where most HP is produced for the gas being used.

I really don`t need to calibrate the SG. When I use it, I just target for the best FE ... so it doesn`t matter how wrong the SG numbers are, as long as they are consistent. Besides that, I have an additional lpg tank which the ECU doesn`t know of - so the SG will get data from the gas tank which is always full.

I think that my SG shows me the actual HP that the engine produces, not the % of power used. At idle I get LOD=2, and when accelerating I get LOD to 30-40.
From what I understand, the BSFC says that my engine ( 1.3 gasoline ) is most efficient between 1800rpm and 2200 rpm, so I try accelerating in this range. On highway driving, I get to 3000 rpm - that is the rpm for 65 mph.

Ok, so I've been playing with the SG and managed to improve my city mpg. From an usual 27 mpg I managed to get to about 33 mpg and on some trips I got close to 35 mpg. I did this by using the engine in the 1000 - 1500 rpm. I have to say that the mpg numbers are pretty low, but the driving feeling suffers a lot.
My best consumption was done when the traffic was light, but otherwise it's very hard to keep up with the others using the engine in that rpm range. The engine is small and not very powerful by default, and the lpg doesn't help.
I tried searching for ways to improve the torque in the low rpm area ( at around 1k rpm ), but not much can be done without serious mods to the engine.
The only "tune" that I can think of is messing with the air intake so that I can move the torque curve to lower rpm.
I know that lpg has a high octane and I could mess around with advance but last time I serviced the car, I've been told that the engine pings a lot, so I would rather leave it alone.

Increase the compression ratio and the timing. Then it'll "boss mode."

Propane, LPG, LNG; they're all rather high octane fuels. Converting a regular car to run on it means it runs, sure, but rather half-heartedly for what its being fed.

I`ve noticed something interesting when running on lpg.
It seems that I get better FE going 100 to 110 km/h than going 80 or 90.
I think that it is because the lpg ecu has some problems in the lower rpm. At 105 km/h the engine stays at about 3000 rpm. That is the peak torque rpm - so it seems that the lpg gets along better with the overall car configuration at that rpm.
If I run on gasoline, I get better FE at about 85-90 km/h.

Just did a 881km trip, with about 50km in town driving and the rest on the express.
I used almost 55 liters of lpg. That gives a FE of about 6.25l / 100 km.
It is one of the best FE that I managed to get running on lpg. This time I used the vacuum gauge and kept the vacuum at about 15, with slow acceleration.
With this level of throttle the car would go at about 80 to 85 km/h.
Pretty slow, but eventually I got there.
So the FE would translate to 37.64 MPG ... on lpg.
Considering the price difference between lpg and gasoline, it would come to an equivalent gasoline FE of about 3.6 l/100km ( that is 65.34 MPG ). It`s better than a diesel :p

Is your car a single point LPG system?

My 328i does 270 miles to 50L of LPG driving sensibly,

and 230 flat out..

can you guess which is more fun?

Hey - I've read about your car ( in your posts ).
There is a bit of a difference between our cars :)
Mine has a 1.3 liter engine and a mind-blowing 84 HP from the factory. By now probably 20 of those horses are dead.
But the car goes - I call it donkey - because it`s lazy, grey but keeps on going without requesting too much food.
So the most fun with my car is doing trips ... I've seen most of my country with this car.
I get the best feeling knowing that it is reliable, comfy ( it has very soft suspensions ), and it`s very cheap to run.

The funny fact is, that by using my car, especially on LPG, it`s cheaper for me to use the car than the train or other public transport. And that is for one person using the car - not talking about bringing someone else with me.
Even in city driving, with the low FE, I get the same price going to work as using the public transportation.

Oh - I forgot - my engine is 1.3 sohc MPI ( multi point injection ) and the lpg system is a Tomasetto stag 200.

Plugs / intake
 

Hi everyone,

I'm new on ecomodder and proud to be part of the community ! I just read this thread and have already two questions :
- Is it best to have a cold or warm air intake with LPG ?
- For the spark plugs, do you use the OEM recommended gap or a little bit narrower like few people advise ?

Thank you for your replies !!

Colder plugs, narrower gap.

LPG burns plenty warm already. Don't know how advisable it is to run a WAI.

For me, the WAI would sometimes choke the engine.
Keeping the IAT moderate ( summer-like temperature ) works best.
For my short trips, the WAI helps me warm-up the engine faster, but for the long trips, the power loss is noticeable.

I still use the standard plugs and they work fine.

Iridium/platinum tipped spark plugs for LPG
 

Hi all,
I have a 1.3 Yaris 2007 too converted to LPG, with a STAG QBox, STEFANELLI vaporiser and OMVL FAST injectors, which is the second Yaris I've had converted but this time with no noticeable loss of power on gas. £15 for 30L LPG tends to produce a constant 265 miles mostly urban driving, which is less than half the price of petrol here in the UK.

That said I've put in iridium plugs which are widely available now - given this is an older (yet still very interesting) thread - designed specifically for LPG - NGK were first, [part number: BKR6EIX-LPG, stock number 3356] and Denso followed shortly after, which are reportedly good for 60k miles.
sparkplugs.co.uk/ngk-iridium-spark-plug-bkr6eix-lpg

Basically the LPG plugs have a wider gap with a stronger core to give a bigger spark to ignite LPG while drawing less electrical power to fire. They also have a more heavy duty insulation around the central electrode.

:thumbup:

Makes me wonder if some sort of intake manifold heating would be useful, like it had been in some Brazilian dedicated-ethanol cars.

Reviving dead thread. I'm also LPG converted car driver. I have read a lot about properties of petrol and LPG. You are observing this phenomenon because LPG is burning slower on low to mid rpms compared to petrol and it needs more timing advance as high as additional 12 degrees. Otherwise flame front in cylinder never catches piston head. I also feel that my car revives around 4000 rpms on LPG. There are special devices to correct timing advance on LPG for nineties cars called Timing advance processors on Google. Unfortunately my BMW is newer and the only way to get correct timng is to make custom ECU remap. 7 years ago I eas driving Swedish brick 740 with dumb 2.3 liter petrol engine also converted to LPG basic system. I optimized it to run extra lean on light loads and normal on full load and advanced timing around 8 degrees. The effect was 2 liters per 100 kilometers less LPG consumption than petrol. There was no signs of premature engine wea.

Search on Google "lpg timing advance processor". You will also get graph of optimized timing.

It seems like the electronic hardware is pretty much similar from a CNG conversion to an LPG conversion, despite the fact that CNG doesn't require any pre-heating in order to vaporize as LPG seems to do.

lpg spark plugs
 

Ok, bit late for a reply and I am sure you have it well sorted out by now, but for anyone else wondering the best LPG set-up, heres my advice.
LPG is a little bit more dense then petrol, hence a smaller spark plug gap. Also, its recommended to run with (hope I have got this the right way round) cooler plugs as LPG runs hotter. All this being said, I kept my current car OEM on the plugs with no adverse effects.
As for a hotter intake system-NO WAY. Hot air losses energy for the engine as it contains less oxygen per given volume. A lot of LPG systems require you start on petrol to get you up to temp because
1)ECU still may be booting up and may not like the LPG gas just yet
2)Keeps the petrol injectors from blocking up so its worth using them at least once per journey
3)LPG sucks heat from the cooling system. On a very cold morning and without starting with any heat in the water, there is a risk of freezing the pipes
4)as mentioned, LPG is more difficult to ignite, so using the stuff on a warm engine will ensure no miss-fires.

Hello from Romania, I'm the owner of the second car on LPG.

First car was a small Daewoo Matiz, 0.8l 3 cylinder car, 2005/Euro3 engine. Mileage was around 6.5 - 7 l/100km on LPG, driving 90 km/h, not a noticeable big increase in fuel for city driving, maybe going 8l/100km. I had a Tomasetto-Achille sequential LPG injection, the car started on petrol and when the coolant would reach 30C will switch automatically on LPG. The car ran fine from 2010 to 2016, bought it second hand in 2010 for about 1500 Euros, made around 60.000 km with me, no problem, then this year was scrapped (rust started to eat the car, brakes starting to fail, strange sounds from clutch) because the cost of fix the car was higher than the car itself. The engine ran very fine till the end, just eating some extra oil. Switching from petrol to LPG was only a beep, no change in engine sound, no change in speed or power.

I bought last year an Opel Corsa B 1.4i 1997/Euro2 for about 1000 Euros. Older but much serious car, i fit it with LPG right away. The instalation is Tomasetto classic, due to single injector petrol injection. Switching on LPG will begin over 2000 rpm, no matter about coolant temperature. Best technique is to let the engine warm a little before start driving, even in summer. If i start the car in the middle of the summer, switch on LPG then drive 1 km, next time the engine will start poorly. This car have 7.5 - 8 l/100km mileage driving 90-100 km/h, going to 9l/100 km city driving or highway 130km/h.

The old Daewoo Matiz was a slow car, max speed was 125 km/h on GPS, so sometimes I used to stay behind a big truck, drafting. Big trucks almost never brake without reasons and they run 90 km/l limit, but i was afraid to close-in too much because of the ****ty brakes of the Matiz. This car type is known sometimes as "the suppository", but my "suppo" was a great car for running the city streets and finding a parking spot. The little engine was not a very good fuel-saver, having a 0.8l 3 cyl. 50 hp on 800 kg car, but was reliable and never broke down.

It's still somewhat surprising to me that you don't just start it up on LPG like it's done in forklifts.