Exploding CNG driven buss! - Page 1
Forum section: electronics / general

author: MT
author_rank: Super Contributor
timestamp: March 10, 2019, 05:53:41 pm
content: Tesla Lipo fires we all know is troublesome but whats probably more so is CNG tankers and CNG driven devices, today a buss driver in Stockholm drove one into a protection steel barrier infront a tunnel and buss went off. Driver was shipped to hospital. The argument could be that CNG is more dangerous then LIPO but both quite bad.CNG gass off like Tesla Lipo but in much more dramatic way.Another one who seams to gass of upwards.And one in Greece rapidly going off!This recent one firemen tries calm fire but the CNG cylinder starts to flame on both sides.CNG car burn by Dutch Brandweer.And of course the Chinese version...

author: apis
author_rank: Super Contributor
timestamp: March 10, 2019, 06:21:12 pm
content: The last one from China isn't from a gas station, it was a warehouse full of explosive chemicals.But I agree, gas is a pretty dangerous fuel for cars, weather it's hydrogen or natural gas. Would much prefer electric vehicles if it was up to me.

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: March 10, 2019, 06:49:04 pm
content: It's interesting that petrol/gasoline would seem from its chemical properties to be a very dangerous fuel, perhaps more so than CNG, but in practice it has a relatively good safety record when used in vehicles. Point to be learned here is that it's unwise to make assumptions about what will prove safe in practice.

author: langwadt
author_rank: Super Contributor
timestamp: March 10, 2019, 07:04:40 pm
content: Quote from: blueskull on March 10, 2019, 06:37:04 pmsome are high pressure:https://en.wikipedia.org/wiki/Hydrogen_tankThey thing with hydrogen is that it is flammable at almost any concentration

author: nctnico
author_rank: Super Contributor
timestamp: March 10, 2019, 07:19:18 pm
content: Quote from: langwadt on March 10, 2019, 07:04:40 pmUnfortunately the statistics are against you. Hydrogen is used a lot and it has a very good safety record. In the outside hydrogen will rise up quickly and mix with enough air not to stay combustible. In contrast most gasses and fuel vapors are heavier than air and tend to sink to the ground and are more likely to mix into explosive mixtures.Note that the second video (from the top) shows that the safety vent valve on the CNG bus does it's job and allows for a controlled burn of the CNG instead of letting the fuel tank explode.@blueskull: yes the energy content of hydrogen per kg is fantastic compared to everything else.

author: dmills
author_rank: Super Contributor
timestamp: March 10, 2019, 07:39:25 pm
content: But the volumetric energy density of H2 at any pressure you would want to deal with is purely crap. 5kg of H2(g) is a BIG TANK!Yea, cryogenic slush, I know, but then the energy needed for liquification and super cooling are so large as to make the overall cycle efficiency very poor.The stuff is a naff road fuel even if you get away from the Carnot cycle as a means to convert it into useful work.Most of those bus fires were fairly standard bus fires followed by the tank rupture disks working as designed.Regards, Dan.

author: nctnico
author_rank: Super Contributor
timestamp: March 10, 2019, 07:51:22 pm
content: Quote from: dmills on March 10, 2019, 07:39:25 pmA 5kg tank seems to fit just fine in the Toyota Mirai in the place where normally the fuel tank is located. It is all about the pressure.

author: Jr460
author_rank: Regular Contributor
timestamp: March 10, 2019, 08:24:23 pm
content: Quote from: langwadt on March 10, 2019, 07:04:40 pmGreater than 4% and less than 94%. In many applications H2 used for it's good thermal properties and is kept above 98% pure. The biggest problems I've seen has to do with sealing a system from leaks. H2 being so small a light weight, it finds ways out that block other gases. And then the detection of the leak is your next problem. The normal soapy water and looking for bubbles doesn't find the smaller leaks. The way we did it was to dope the system with a bit of helium and then use a portable mass spectrometer tuned for He.

author: janoc
author_rank: Super Contributor
timestamp: March 10, 2019, 08:42:34 pm
content: Quote from: MT on March 10, 2019, 05:53:41 pmThe same sort of thing can happen even with regular diesel. If a fuel tank is ruptured on impact, an enormous fireball is very likely - just look at the recent train crash in Cairo where an engine ran into buffers. The fuel tank ruptured and KABOOM, over 20 dead and many injured in the resulting fireball. Another famous crash that resulted in diesel exploding was the Ladbroke Grove disaster:https://en.wikipedia.org/wiki/Ladbroke_Grove_rail_crashIt happens quite often in truck crashes too but there it usually "only" starts a massive fire and doesn't explode.CNG is a very safe tech routinely used on city buses and public transport because of both costs and much lower emissions than diesel. Furthermore existing buses can be relatively easily converted to CNG, that's what makes it attractive for the transportation companies because they don't need to replace buses (uber expensive) when faced with emission-based traffic restrictions in cities. Purely battery powered electric buses are not really an option yet - the battery capacity is insufficient to run large capacity vehicles for several hours that would be required.Bus fires due to mechanical problems are quite common (regardless of fuel type) but these kinds of spectacular incidents are extremely rare. Let's not blow things out of proportion here, especially given that this was not caused by the fuel but by the bus crashing into an obstacle and rupturing the fuel tank.

author: nctnico
author_rank: Super Contributor
timestamp: March 10, 2019, 08:52:18 pm
content: Well don't rule electric busses out yet. Where I live there are several electric busses driving around (made by BYD from China). It seems these have a range of 250km to 300km and get charged at night.

author: langwadt
author_rank: Super Contributor
timestamp: March 10, 2019, 09:19:25 pm
content: Quote from: nctnico on March 10, 2019, 08:52:18 pmthere are places that use busses that charge via pantograph at the end station, only takes a few minutes to charge enough for morethan a round trip

author: apis
author_rank: Super Contributor
timestamp: March 10, 2019, 09:57:01 pm
content: We have battery electric busses here as well in a few places, it is supposed to work well. Only problem is during winter in the far north where they need diesel space heaters during winter, but you can use biofuel for that so it's still renewable.

author: janoc
author_rank: Super Contributor
timestamp: March 10, 2019, 10:20:50 pm
content: Quote from: langwadt on March 10, 2019, 09:19:25 pmYes but that's not usable everywhere. Trolleybuses also exist, as do hybrid diesel/electric buses. But each have their own issues, mostly the infrastructure (overhead wires being an eyesore and not cheap to put up + energy distribution is needed, it also severely limits where the buses can go). The diesel/electric hybrids are good only for short trips on electric power.Heck, there were even buses that ran using flywheels - the flywheel was spun up at a stop using electric power and then powered the bus until the next stop. It didn't exactly take hold ...https://en.wikipedia.org/wiki/GyrobusAnd fully electric battery powered vehicles are still very expensive, compared to regular ones (almost 60% more). Not exactly a very appealing proposition to transport companies facing upgrades/replacements of large fleets.I am not writing them off but purely electric buses being a widespread alternative to diesel or CNG is still quite a few years off except for small vehicles.

author: langwadt
author_rank: Super Contributor
timestamp: March 10, 2019, 10:49:30 pm
content: Quote from: janoc on March 10, 2019, 10:20:50 pmI think most city busses here have a round trip of less than 30km, a pantograph super charger at the end could easily charge it for around trip in a few minutes. Only infrastructure needed is enough power at the charging station and it could be used for charging cars when the bus isn't there

author: vk6zgo
author_rank: Super Contributor
timestamp: March 10, 2019, 11:20:48 pm
content: Quote from: janoc on March 10, 2019, 08:42:34 pmWe've been running CNG buses in Perth WA for decades, & although there have been a few impressive "burn ups", these have been very rare, with no injuries, so considering the thousands of km covered, are a pretty good trade off.We had a couple of "Eco-busses" running, using hydrogen & a fuel cell, but the cells tend to fail after a while.

author: wraper
author_rank: Unknown
timestamp: March 10, 2019, 11:23:47 pm
content: Rear seats have nice passenger ejection system underneath.Quote from: nctnico on March 10, 2019, 07:51:22 pm

author: duak
author_rank: Super Contributor
timestamp: March 10, 2019, 11:34:08 pm
content: I remember seeing a newspaper headline "BARBEQUE EXPLODES, TWO LAND IN HOSPITAL". Now there's a vivid thought. Perhaps it could be trotted out and retooled in case the previous post come true.

author: apis
author_rank: Super Contributor
timestamp: March 11, 2019, 12:32:57 am
content: Quote from: janoc on March 10, 2019, 10:20:50 pmThey began testing with 100% battery electric city busses in a nearby city in 2016, last year they began expanding to other cities. Found out now that they are planing to replace most city busses with battery electric by 2030.These are also made by BYD.There's also a battery hybrid ferry nearby:

author: Mr. Scram
author_rank: Super Contributor
timestamp: March 11, 2019, 01:09:58 am
content: You'd almost think that storing energy densely comes with some risks.

author: MT
author_rank: Super Contributor
timestamp: March 11, 2019, 02:34:35 am
content: Quote from: apis on March 10, 2019, 06:21:12 pmYes i know, i just felt for some exaggeration! Chinese the best at staging unexpected explosions!Quote from: wraper on March 10, 2019, 11:23:47 pmLPG, Russia.https://youtu.be/5-nOPvXiIWQ?t=33

author: wraper
author_rank: Unknown
timestamp: March 11, 2019, 02:49:03 am
content: Quote from: MT on March 11, 2019, 02:34:35 amLPG has up to about 10 bar pressure when tank gets quite warm, in that case tank was placed inside the trunk. Toyota Mirai has tank sitting right under the rear seats.https://ssl.toyota.com/mirai/assets/modules/carpagehowitworks/Docs/MY18_Mirai_eBrochure_FuelCellTech.pdfQuoteVery nice knowing there is a tank under 750 Bar placed beneath your ass. If it ruptures ejection is almost guaranteed.

author: wraper
author_rank: Unknown
timestamp: March 11, 2019, 02:55:53 am
content: Quote

author: MT
author_rank: Super Contributor
timestamp: March 11, 2019, 03:05:06 am
content: Toyota Rav4 flaming out, is it the petrol tank or the bat electrolyte or both or neither?!This is supposedly the batt pack in the chassis.

author: raptor1956
author_rank: Frequent Contributor
timestamp: March 11, 2019, 06:12:08 am
content: Quote from: IanMacdonald on March 10, 2019, 06:49:04 pmThere have been many cases of cars going up in flames due to problems with the gasoline (petrol) tank. Several models of car like the Ford Pinto were renowned for going up at the slightest provocation. But, with time they've managed to improve safety so major problems are mostly a thing of the past. With time electric cars will improve the fire risks and if CHG became a major fuel option I could see improvements made there to. From a pure energy standpoint petrol and diesel are both very energy dense and petrol in particular can burst into flames explosively under the right conditions.Brian

author: Berni
author_rank: Super Contributor
timestamp: March 11, 2019, 07:10:11 am
content: Dang... over here these CNG fueled buses are getting more and more popular too.My car is modified to run on LPG since the stuff is 50% the price of gasoline, but that stuff is much safer. The problem with CNG is that it has to be kept under a huge amount of pressure to be able to fit a reasonable amount of it into a tank. These large tanks typically operate at 25 bar! If they get hot (such as in a fire) these tanks can rise to many times that pressure. So when such a tank fails it is like a few sticks of dynamite going off from the pressure alone, let alone the gas then igniting.On the other hang LPG is much safer because it only takes a few bar to liquefy it (Even a normal soda bottle can contain liquefied LPG, but don't do that for obvious reasons) and is popularly used to run gas stoves and gas grills all over the world. The tank is easily way overbuilt for these pressures and if a leak happens its just a loud hissing before the tank cools down rapidly and goes cryogenic, limiting the amount of output (If there is not a safety valve that stops the flow before that). However its still very dangerous if a LPG tank ends up in a fire, it can build pressure faster than a relief valve can cope and cause it to explode with a lot of energy.

author: apis
author_rank: Super Contributor
timestamp: March 11, 2019, 08:46:12 am
content: Yeah, pretty amazing. They didn't begin using full electric drive until november last year, so probably why there haven't been more news about it yet. Norway also has an electric ferry:https://www.theexplorer.no/solutions/ampere--the-worlds-first-electric-car-and-passenger-ferry/?gclid=EAIaIQobChMIq-__otn54AIVyYeyCh2DjgClEAAYASAAEgLNA_D_BwE

author: janoc
author_rank: Super Contributor
timestamp: March 11, 2019, 09:27:18 pm
content: Quote from: langwadt on March 10, 2019, 10:49:30 pmI was thinking more places like Paris where the bus is passing through the city center (otherwise no point bothering with an electric one) and spends a lot of time slowly advancing through traffic jams and navigating the dense traffic in the narrow city streets. The distance traveled may be even much less than those 30km or so but the energy requirements are high, especially in the summer where the requirement is to have AC in the new buses (you could literally die in the summer heat in Paris when the August heatwaves hit ...)The termini typically serve many vehicles/lines at once, with rapid turnaround. So you can't just "put the bus on the charger" there for 15-20 minutes, the terminus would have to be enormous to accommodate this. The same for the lines that have termini in the city center - trying to put overhead wires and what not there would cause a huge uproar (historic center and all that) - and that assumes you would have the space to begin with.Parisian RATP (the transportation company) has, in fact, a huge headache with this now because Paris is progressively banning diesels from the city. And they still run a lot of buses that don't fulfill even the old Euro emission standards. We are talking a fleet of about 4000 buses in the streets every day, not counting private operators, tour buses and long distance transport (Eurolines, Flixbus and similar). That's an enormous amount of money required - which simply isn't there. AFAIK, they are putting more money into CNG buses and are investing into a common project with Enedis (French electricity distribution company) to develop electric buses suitable for these conditions but it is only just starting now.

author: janoc
author_rank: Super Contributor
timestamp: March 11, 2019, 09:40:48 pm
content: Quote from: MT on March 11, 2019, 03:05:06 amBattery electrolyte isn't flamable (at least if we are talking normal lead acid car battery) - that's sulfuric acid + water.The video shows a bleve of a petrol tank. I had the "pleasure" to witness this first hand few times. Yobs love to set cars on fire for fun here (yay France) and when the car burns for a while, the tank will heat up and pressurize until it (or the fuel pipe) bursts - that's what you see. It is not really an explosion in true sense (detonation) but the pressurized fuel vapors escaping the ruptured tank and igniting with a large WHOOSH (and sometimes a bang of the tank bursting).An even worse event that will eventually happen if the fire isn't extinguished rapidly is the tires bursting in the heat - that's an enormous BANG and it sends shrapnel all over the place.These firemen have only themselves to blame there, IMO.Here when the fire crew arrives on the scene and it is obvious that the car is burning for a while already, they willneverapproach the vehicle on foot. They can't know when will the tank or tires blow. That could cause a serious injury or even kill a man, despite full protective gear. They will always use the water cannon from the truck first to reduce the fire and to cool the vehicle down from distance. Only then they approach on foot with the hoses to finish the job.

author: Refrigerator
author_rank: Super Contributor
timestamp: March 11, 2019, 10:00:41 pm
content: I drive LPG and it's pretty safe unless you make it unsafe.To get your LPG modded car through MOT you have to pay more and there are more tests to run.But i love the fact that LPG is so cheap, around here it's 2.6x cheaper than gasoline (per liter) and you only burn about 30% more compared to gasoline, in the end it turns out to be significantly cheaper than even diesel.To me personally the low-ish pressure of LPG is a bit of a problem since when my turbo spools up it tends to overpower the LPG systemAlso if they want an electric bus then why not get a trolleybus?We still have ancient trolleybuses making their way around the city here and the torque on those bastards, holy crap, when you get on board you better grab onto something before it starts moving or else your next destination is the floor

author: wraper
author_rank: Unknown
timestamp: March 11, 2019, 11:49:54 pm
content: Quote from: Refrigerator on March 11, 2019, 10:00:41 pmBecause you need to build infrastructure and they are way less versatile.

author: MT
author_rank: Super Contributor
timestamp: March 12, 2019, 12:32:58 am
content: Quote from: janoc on March 11, 2019, 09:40:48 pmYes electrolyte burns , look at the RAV4 picture, thats whats discussed, 386V lithium-ion battery of 4,500 cells rated at 41.8 kWh maximum power output of 129 kW. Similar tech as Tesla S.

author: Berni
author_rank: Super Contributor
timestamp: March 12, 2019, 06:10:20 am
content: Battery electrolyte is always nasty stuff.Most of the time its just corrosive as hell such as the sulfuric acid used in lead acid batteries. But for rechargeable lithium batteries its indeed very flammable too, to make it worse it also tends to have a fairly low flash point so any sort of battery failure is likely to ignite it on fire.Hopefully a better battery technology will come around before electric cars really take off, but inherently anything storing a lot of energy inside of it is dangerous in some way (But some are more dangerous than others in a failure mode).

author: apis
author_rank: Super Contributor
timestamp: March 12, 2019, 12:54:11 pm
content: Quote from: wraper on March 11, 2019, 11:49:54 pmTrolleybuses are not so bad, especially if combined with a battery. Then you only need to invest in overhead wires for the busiest parts of the routes, you still have some flexibility to make route changes and the battery can be charged while driving.They tested a trolleybus here as well, but settled on battery electric since it was cheaper and the battery busses have a range of 250 km which is good enough for the city buses anyway. (I assume they meant cheaper short term, because no one wants to plan ahead more than a few years these days and therefore the investment in infrastructure becomes cost prohibitive.)

author: Gromitt
author_rank: Regular Contributor
timestamp: March 13, 2019, 04:35:20 pm
content: Quote from: apis on March 12, 2019, 12:54:11 pmThere is a city in Sweden that has trolleybusses, Landskrona. Has run since 2003.

author: MT
author_rank: Super Contributor
timestamp: March 13, 2019, 05:03:28 pm
content: Wire buss Gothembourg 1940!