Nissan Cima CNG conversion!

[Zuikkis]

Hi,

I converted my Cima to run on natural gas (CNG). It still runs on gasoline too, if needed, because CNG is not yet so widely available. I used a DreamJet 8cyl kit, from AutoGas Italia. All parts and tanks were bought from CNG House in Finland, http://www.cnghouse.fi/

All photos (and some more) can be found in larger size at http://zuik.org/galleria?gallery=/Autot/CimaCNG

CNG is different than LPG that you might be more familiar with. The biggest difference is that CNG doesn't get liquid when compressed, and so it takes a lot more space. The tanks are HUGE. Obvious problem was where to fit any sensibly large tank without using all of trunk. CNGHouse had some different size tanks available. After some measurement and careful thinking, I ordered one 50 liter and one 57 liter tank.. They are quite large, they weight over 100kg when empty. They can take about 17kg of gas, which gives you about 250km (150miles) of mileage. You can continue with normal gasoline after that, of course.

First problem was that I had previously installed K-Sport air suspension, and the spare tire place was used by the air tank and compressor. I made a smaller air tank from an old fire extinguisher, and managed to fit the tank, compressor and the solenoids to the side of the trunk..


http://zuik.org/galleria?gallery=/Autot ... CN0024.JPG

Next, we modified the exhaust system, from rear axle to the back. I was surprised how little change there was to the car sound? Old muffler was huge, and now it was replaced with two smaller flow-thru mufflers.. Yet there really is no big change, the car is still very quiet. I guess the original mufflers at the start of the exhaust are doing their job well..

The image below looks funny. A lot of empty space available, yet all the exhaust pipes are stuffed to small place at the side for some (not yet so obvious) reason..


http://zuik.org/galleria?gallery=/Autot ... CN0034.JPG

Then, the dangerous part. This really took some thinking and measuring, because you really can't back up from this point. Then I just took my angle grinder and started cutting...


http://zuik.org/galleria?gallery=/Autot ... CN0100.JPG

The new floor for the trunk below.. This was simply welded together, then painted. I decided to NOT weld this to the car, instead I used lots of car body glue (?) and rivets.. I know this is questionable method.


http://zuik.org/galleria?gallery=/Autot ... CN0104.JPG

Below is the holding bracket for the tanks. It is designed so that it rests above the car body bars, and is bolted through it. There is no weight on the trunk floor, this bracket takes all the weight of the tanks to the body bars.. Also it will stiffen the body because it is bolted tightly to the bars.


http://zuik.org/galleria?gallery=/Autot ... CN0105.JPG

Tanks finally in place!


http://zuik.org/galleria?gallery=/Autot ... CN0131.JPG

[Zuikkis]

With the tanks in place, now it's time to modify the engine room.. I removed the plenum, and drilled holes for the CNG injector nozzles. They are simply hose nipples, the actual injectors are in the injector rail separately..

Below you can see the installed nipples in place. I used a lot of thread locking glue to make sure they are tight..


http://zuik.org/galleria?gallery=/Autot ... CN0294.JPG

Plenum re-installed.. The blue line is the CNG line from the trunk. It comes to the big thingy that looks like Millenium Falcon, it's a pressure reducer.. CNG tanks hold 200bar of pressure (about 2800 psi), this reducer drops the pressure to 1bar (14psi). Then the low pressure hoses goes to the blue CNG injectors.

I actually had to add another of these reducers because one wouldn't flow enough at high rpm..


http://zuik.org/galleria?gallery=/Autot ... CN0295.JPG

[Zuikkis]

http://zuik.org/galleria?gallery=/Autot ... CN0129.jpg

Final photo of the car.. I tried to photoshop it slightly lighter to show how much (or little) the new trunk floor is showing behind the rear bumper. Not too bad..

It has been now working for two months and I have been quite happy with the system. It costs perhaps 40% of gasoline price to drive with CNG, so the system should pay itself in less than two year with my annual driving..

Most of Finland's CNG is natural gas (methane) which comes from the dinosaurs just like oil. However there are a few places which supply "biogas" which is made from cow s*it and other garbage..

Biogas is interesting because it has zero co2 emissions. Not that I really care for that, but it's super cool to drive by some moron Prius driver and ask if he cares for the environment with his hugely polluting car, while I drive away happily with my "zero emission" 4.1 liter V8...

Edit: fixed the image link..

[tfitzs01]

Good looking conversion. Here in the states CNG is readily available if you know where to look.

But the zero CO2 statement is wrong. Any hydrocarbon that is burned has carbon dioxide and water as its primary waste products

CNG is essentially compressed methane that when burned with oxygen produces carbon dioxide and water.

CH4 + 2(O2) = C02 + 2(H2O)

Lot of science here, but CO2 is not a very good radiant emitter of heat energy (infrared or IR), or greenhouse gas, due to its linear chemical structure that only permits a temporary dipole moment (uneven charge in the structure) that is capable of emitting IR energy. But this dipole moment is very temporary (picoseconds). Water has a permanent dipole moment and is capable of emitting and storing much more IR heat energy. So the political nature of global warming alarmists will have you believe that it is primarily one gas, CO2, that is raising temperatures, it is actually a very complex process that we do not understand yet. Especially if you consider that accurate thermometers have only been present the last 75 years or so, and satellite measurements for the past 50. Hard to judge millennia of temperature data with but 75 years of accurate data. (and many of these thermometers are at airports next to the runways too). Off my soapbox.

But at least your car both looks much cooler than the Prius, and your batteries when they need to be swapped out won't cost half the car's value at new! So money saved in your wallet!

[lino]

It has been now working for two months and I have been quite happy with the system. It costs perhaps 40% of gasoline price to drive with CNG, so the system should pay itself in less than two year with my annual driving.

Nice write-up . I never thought about doing any kind of conversion before. I know my mechanic does a lot of gas to diesel conversions for Mercedes owners, but I've never seen a CNG conversion before, especially not on an Infiniti.

You say that you are saving substantially with the new system, but I'm wondering are you saving that much even taking into consideration all the additional weight?

[Zuikkis]

But the zero CO2 statement is wrong. Any hydrocarbon that is burned has carbon dioxide and water as its primary waste products

CNG is essentially compressed methane that when burned with oxygen produces carbon dioxide and water.

CH4 + 2(O2) = C02 + 2(H2O)

Yeah, this is true, no arguing really.

But the Biogas' advertised zero-CO2 comes from the fact that it's made from garbage that otherwise would be unused.. Cow dung or any garbage dump will release lots of methane, which will convert to co2 when it reacts with sunlight ond O2 in the air. Same amount of CO2 is generated if you take the methane and use it in your car..

Most of the garbage dumps in the world don't have any sort of methane "pickup" systems, the methane is simply lost to the skies. This would be "co2-free" fuel for our cars. The only way to stop this methane supply would be to stop producing garbage, and that seems to be difficult.

[Zuikkis]

You say that you are saving substantially with the new system, but I'm wondering are you saving that much even taking into consideration all the additional weight?

Yes, that was already in the calculations.

I know you use mpg figures in the States, but let's try with european values anyway..

With gasoline, before the conversion, Cima used about 11.5l/100km in average. After the conversion, with all the extra weight, CNG consumption is 6-7kg/100km, about 6.5kg/100km in average.

Gasoline price is ridiculous here, about 1.40 EUR/liter.. So 11.5*1.40 gives 16.10 EUR / 100km.

CNG price is currently 1.12 EUR/kg. Again, 6.5*1.12 = 7.28 EUR / 100km. Well, it's about 45% of gasoline price.

[wingFeather]

Awesome!

[Q451990]

Wow!!!!!

My only concern would be having those canisters of explosive gas at 2800PSI sitting back there if I got rear-ended... Did you consider putting the CNG tanks in the current well protected gas tank location behind the back seat, and going with a more traditional bottom-mount fuel tank in your trunk location?

How is the car's performance when running on CNG vs. gasoline fuel?

Again... wow!

Heath

[Zuikkis]

Wow!!!!!

My only concern would be having those canisters of explosive gas at 2800PSI sitting back there if I got rear-ended... Did you consider putting the CNG tanks in the current well protected gas tank location behind the back seat, and going with a more traditional bottom-mount fuel tank in your trunk location?

How is the car's performance when running on CNG vs. gasoline fuel?

Again... wow!

Heath

Yes my original plan was to put CNG tank in the place of the normal fuel tank. However there's actually quite little space there! The rear strut towers are so close to each other that the tank would need to be really short, and you could only really fit one. I found a 45L tank that probably would have fitted, but now I have 107L which means more than double the mileage.

However I really doubt that these tanks would crack even if you drop them from aeroplane.. The wall is something like half an inch thick, solid steel. That's why they weight 60kg each (130lbs or something).. What's more, methane is lighter than air, so any leak will escape straight up to the sky, unlike LPG which is heavier than air and would fill the car with explosive humes.

Car performance is crap with CNG, it feels like nothing happens when you hit the throttle. However the CNG injector ECU allows you to set a rpm limit and switch to gasoline at that revs. I set the limit to 4000rpm. This usually means that when you hit the throttle (kickdown), it switches to gasoline almost immediately and you have full power when overtaking etc, then it switches immediately back to CNG when you're done.. Or you can simply switch it to gasoline manually when needed, there's a simple push button for that.

CNG is something like 135 octane, which would allow much higher compression ratios and ignition advance. I suspect that if you really built the engine for CNG, you would get higher power than with gasoline.. But such engine wouldn't run with gasoline anymore.

I did actually advance the ignition slightly by turning the CAS sensor. I started using high octane fuel, and checked with detonation earphones that there is no detonation when driving with gasoline..

[Emsea]

Just don't blow a tire haha. Very well done, I like that idea a lot. Especially when you used a fire extinguisher for your airride. Good thinking all around.

If you don't mind my asking, how much (approx.) did you have to invest for your twin millenium falcons? (Actually, just total invested price is what I'd rather know, I just wanted to say 'twin millenium falcons' lol)

[Zuikkis]

Just don't blow a tire haha. Very well done, I like that idea a lot. Especially when you used a fire extinguisher for your airride. Good thinking all around.

If you don't mind my asking, how much (approx.) did you have to invest for your twin millenium falcons? (Actually, just total invested price is what I'd rather know, I just wanted to say 'twin millenium falcons' lol)

I actually just blew a tire a few weeks ago. It's obvious to happen now when you don't have a spare tire, never happened before..

The parts cost about 2500 EUR (>$3000).. It sounds a bit expensive, but given the Finnish gasoline prices, it only takes about 20000km (12000 miles) to get the price back. And then there's of course something like 20h of work, which I didn't take into account..

[Emsea]

Hahaha well I apologize for jinxing you. That sounds quite reasonable as far as price goes, as for self-labour, it's always free, no matter how painstakingly long it is haha.