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offroadwolf1
Active Member
25 Posts |
 Posted - 02/05/2013 : 3:28:38 PM
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| I have been reading a lot about different schools that are looking into both CNG and LNG vehicles. The only difference in these is Compressed fuel runs 3000 to 4000 psi in the fuel tanks, liqued fuel is stored at 250 degrees below zero to keep it in a liqued state. Both have ups and downs to each fuel type and if your thinking about switching to either of these you really want to do your homework. Compressed fuel is stored in a high pressure tank and regulated down for the engine to run it, liqued fuel is warmed so the engine can use it, both end up right around 100 psi at the engine. An alt fuel engine is very similar to its diesel conterpart but lower compression and spark plugs. These engines are also extremely more complex and problematic then diesels. The big factor a lot of people forget when looking at them is cost. They run different engine oil than the diesel and a lot of the components are more expensive. The experience I have had with them is a fleet of 400 of them, and the fuel mileage ended up at best half of what the diesels got. The other problem we faced is when the fuel station breaks there is no back up plan, you cant run down the street and fuel em up. |
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bwest
Administrator
United States
1805 Posts |
Posted - 02/05/2013 : 7:02:19 PM
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| Thanks for the info. I have been interested in the facts of CNG as of late. Seems like every time I mention propane I get a question on natural gas too. |
Bryan |
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Doug K
Active Member
44 Posts |
Posted - 02/06/2013 : 07:47:10 AM
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One of school districts here in the BC interior went to ng. I believe it cost them in excess of a quarter million to make the necessary modifications to their shop, set up a pump station, get the tech's qualified etc.
I guess ng would be fine if all your buses did was their regular runs, but if you are like us, we got buses running all over the country on weekends and I have yet to see an ng filling station.
Personally ng kinda scares me, those are some pretty wild pressures you are working with. |
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offroadwolf1
Active Member
25 Posts |
Posted - 02/06/2013 : 08:48:14 AM
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I have noticed the school bus industry leans towards compressed gas versus liqued. Natural gas is not as dangerous as everyone thinks. Natural gas will not ignite unless it has reached around 14 percent gas and 86 percent air. This gas will not ignite if its too rich or too lean. If a leak occurs under pressure and you try to ignite it it will blow the flame out do the the higher pressure. The tanks the fuel is in are very strong. But a little caution needs to be taken since the fuel tank will hold 4000 psi. It regulates down from the tank and then down again prior to entering the engine. This is where training comes in knowing what fuel pressure is where. We went through all the same fears when we first got natural gas vehicles. Believe it or not your propane is more volitile than natural gas, it has a much higher boiling point, around 30 degrees and don't quote me on it, so if its cold outside propane will sit on the ground like fog, but it can be lit very easyily by any spark. With training and time the techs in the shop will become comfortable with the fuel and understand all the dangers they worry about are about the same as a gasoline engine.
Our school will not be going to an alternative fuel bus. I have seen the cost and problems they bring and right now the technology is just not there yet. Cost is higher, and I can't send them out of town because we couldnt fuel them. Another note to make is fueling time on a CNG vehicle. I beleive the new fast fill systems take about 30 to 45 mins to fill one vehicle. The slower systems take several hours. |
Edited by - offroadwolf1 on 02/06/2013 08:50:42 AM |
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bwest
Administrator
United States
1805 Posts |
Posted - 02/06/2013 : 12:13:45 PM
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| Here again I think propane shines. Takes about the same amount of time as fueling a diesel. There are places to fuel on the road. It is not as easy to ignite as you are saying. I don't know the percentages right off the top of my head but I'll try to post them. Common sense (which seems to be less common lately) tells me propane is the answer, but I think you know what they say about opinions. lol |
Bryan |
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Doug K
Active Member
44 Posts |
Posted - 02/07/2013 : 07:25:09 AM
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| I am happy with the status quo, diesel. It is sold everywhere, propane is limited,cng is pretty much non existent. To me going to propane would be like going back to gasoline engines (it was a happy day when we got rid of the last of those sob's). I am so glad not to be *ing around with spark plugs and plug wires,distributors, pick up coils ect. Cummins diesel engines are bomber, other than regular maintenance we rarely have to touch them. I know you can argue propane engines last longer, but in our case the rest of the bus rots out long before we have engine issues. |
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partsman_ba
Advanced Member
United States
219 Posts |
Posted - 02/07/2013 : 09:12:24 AM
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@Doug K, have you not had problems with Cummins ISC CAPS injection pumps? We keep an ICV valve and accumulator on the shelf, we've had so many failures. Probably because of the low sulfur diesel, but still...
Or, haven't you cursed the day they mandated all that emissions crap on the exhaust side? I've got ISB 2-piece exhaust manifolds leaking on regen, DPF's clogging up, DEF dosing system failures, etc. |
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bwest
Administrator
United States
1805 Posts |
Posted - 02/07/2013 : 09:39:56 AM
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| Doug, I too was glad to see the gasers go. I hated the 366 GM that burned off the plug wires. I hated dealing with the carburetor problems. I was annoyed every time I had to figure out if the ignition problem was a pick up coil, the main coil or some other electrical part. But with the new emissions these propanes are the lesser of the evils. But keep in mind, gone are the days of the distributor and pick up coils. Also gone is the annoying carburetors. There is really no reason for a bus company or district to look into propane. It fits our application so well. Now, there may be an area of the country that it's a bad fit for some reason but I haven't heard of that yet. Oh, don't let your drivers get in one if you don't want to hear them wanting one. All the drivers who have ever been in my propane want one. |
Bryan |
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Doug K
Active Member
44 Posts |
Posted - 02/07/2013 : 2:08:18 PM
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I have changed a few CAPS pumps on ISC, but always because the shaft broke. I had some issues with the accumulator pressure sensors, but I seem to recall they came up with a fix for it(a different wire harness and sensor I think) and never had issues after that. One ate a camshaft some years ago, all I can attribute that to is a faulty camshaft. CAPS are a thing of the past now too. I still have a half dozen old buses with them.
I have yet to have any real issues with common rail injection used today. The majority of problems I have had have been in the calibration. Some of the first vgt turbos failed (warranty) but haven't had a problem with one for some time now.
I have 4 buses with the SCR system on them 2 ISC's and 2 ISB's and again the only problems so far have been in the programming (knock on wood )
The first ones with regen systems we had issues with the catylist faces plugging and also particulate filters plugging prematurely. This again was all in the calibration, once Cummins finally came up with the right program the problems ended.
I admit I know nothing about today's propane systems. The only propane systems I ever had much to do with were probably early 90's automotive conversions. I'm sure they have come a long way since then, |
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bwest
Administrator
United States
1805 Posts |
Posted - 02/07/2013 : 3:41:39 PM
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| Quick run down on propane system. Pump inside tank pumps fuel under pressure as a liquid to the injection rail. Injectors are fired by the computer and fuel changes to vapor after it's injected. No freezing up, no problems in winter. |
Bryan |
Edited by - bwest on 02/08/2013 09:35:28 AM |
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Topic |
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Natural Gas Buses
