Great Western Coffee Shop

One of the rotating banners on FGW's front page at the moment proudly states that the MTU engines have reduced CO2 emissions by 64% and smoke emissions by 42%, I assume compared to the Paxman Valentas they replaced.

Now, I can well believe the statistic on smoke, and in fact when I think back to BRI-PAD Valenta-engined HSTs pulling out of Temple Meads when they'd been idling for a while, I'm amazed the reduction isn't greater than 42%.

The one that puzzles me is the CO2 statistic. As lots of you no doubt are aware, diesel is (to a first approximation, anyway) a fuel composed of hydrocarbons, for which CO2 and water are the products of complete combustion. I find it a bit surprising therefore that a 64% reduction on CO2 emissions is being quoted because that suggests to me (again, to a first approximation) that the MTU engines are using 64% les fuel than the Valentas.

They're undoubtedly hugely impressive in terms of power output, low noise and low emissions, but are the MTU engines really that much more fuel-efficient or have the press office got CO2 emissions confused with some other pollutant (e.g. carbon monoxide, CO, perhaps?)

An interesting question. Presumably due to better efficiency, less combustion is required to output the same power.

i belive they use 15% less fuel

I am always very wary of percentages just being quoted out of thin air. To be valid there needs to be accompanying information on the circumstances under which these percentages were calculated.

If I go out for a walk down a busy road wearing a hi-vis jacket the probability of me being run over is 1%; If I take off my jacket the probability is now 2%.
I have increased the probability of being run over by 1%, from 1% to 2%. But no ! I have doubled the probability from 1% to 2%, a 100% increase. Both are equally correct - or incorrect !

There are railway versions of this engine which allow half the cylinders to be shut down at idle. That's 50% accounted for; they use 15% less fuel; therefore 50% plus 15% = 64% (almost !)  I can prove anything ! Easy !

i've heard figures of 14%, 9% and "up to 20%" so 15% sounds about right (although it will also depend on time-speed, driving technique, passenger loading etc)

  But do the statistics take into account the extra stops like Ivybridge, Saltash etc.
 
 I was led to believe the engines used most of their fuel when stopping/starting from stations.

Its the starting that uses the fuel.  Stopping uses breakpads. 

The "extra stops" at low-speed locations (certainly Saltash in one of those because of the 15 (?) mph limit on the bridge) probably don't use much extra fuel.

The MTU engines do indeed burn less fuel and therefore emit less carbon dioxide, however the figure normally quoted is about 15/20%, worthwhile certainly, but nothing like 64%.

I would suspect that the 64% is either a mistake, or is under some particularly favourable condition not typical use.

Or perhaps they mean a 64% reduction per passenger per mile? that might be just about possible on a set with high density bus seating and no catering vehicle.

64% less CO2 is definately a mistake.  The FGW website admits 15% less fuel consumption so CO2 reductions would be similar.

I suspect that the 64% reduction applies to CO (ie, carbon MONOXIDE) reduction.  I could well believe that a cleaner burn achieves that.  less CO is good because it is a nasty poisonouus gas, but not relevent from a green house gas perspective.

I imagine it was an honest mistake by someone without the chemisty knowledge to appreciate the difference between CO and CO2

unless there has been an incredible breakthrew in exhaust systems... maybee atmos does exist?  ;)

I'm NOT inclined to believe any thing like 50% reduction.

IF the MTU engines are so good why are HST power cars STILL BANNED from entering Penzance Train shed?

Vovagers and all units are allowed into Penzance train shed.

So is FGW telling porkies about emission reduction, or just incompetent that they haven't lifted the HST ban on Penzance?

Hmm.  In the past, I'd have dropped an e-mail on this subject to Andrew Griffiths at FGW, but ... http://www.firstgreatwestern.info/coffeeshop/index.php?topic=4870.msg44448#msg44448  ::)

The 64% figure may be when idling. Starting a Valenta was a mucky business as the Paddington shed roof still bears witness.

The on-load saving (c15%) is due many things; better injector atomisation, better fuel/air mixing, better flame spread and microprocessor control of everything plus tight regulation of use patterns.

Pity the accountants stopped UK engineers developing an equivalent.

OTC

That could be the answer. I think the MTU reverts from a 16-Cylinder engine to an 8-Cylinder engine when idling. I'm no expert on engines, but might that 50% difference and a more efficient engine give the figure quoted?

The MTU reverts to idling on 8 cylinders. The 8 cylinders in use are alternated every so often in order to even up the wear and tear. This occurs every 5 minutes. The Valenta was also fitted up for single bank idling in later life, 6 cylinders were cut out when the F&R was moved to engine only. Idling on fewer cylinders gives you better combustion of the fuel, due to the increased mechanical load on them which reduces the amount of clag from partly burnt fuel and any lubricant that might have found its way into the combustion chamber. This was a fairly significant issue on the Valenta if left idling for extended periods.