HST fuel consumption

[BRX]

10x seems implausible even for 2+7 vs 3 car. The 5x guesstimate comes from those figures - and we have no source for those figures. They might as well be pulled from the air.

 

[Bald Rick]

The almost 10 x figure I quoted was for a 2+7 HST v 3 car 170 which isn't whats being used. My best guesstimate was x5 for a 2 +4 vice a 3 car 170 or around x4on a per seat basis. The per seat basis is worse because much of the increased seats are first class.
A 2+4 HST weighs around the same as a 6 car 170 but has 3358KW power vice 1890KW for 6 car 170. A 6 car 170 would have a lot more seats.
The HSTs are a vanity project for Scotrail to have an internal "Intercity" network but they certainly aren't green.

But the physics will be that the 4,500hp on an HST is applied for less time than the lower power on the 170, if the trains are keeping to the same schedules. At a base level there’s only four reasons why fuel consumption would be more per seat in an HST than a 170

1) the train weighs more per seat, needing more diesel to shift it,
2) the train has more seats, needing more diesel to shift them overall,
3) the engines / transmission are less efficient in turning diesel into movement,
4) the train is required to operate to a faster schedule (ie better acceleration, more time at higher speeds), requiring more diesel to meet the schedule

1) & 2) are simple to calculate, 3) is simple if you know the relevant efficiency numbers, and 4) needs some clever modelling or impirical testing.

 

[paul1609]

1) HST (2 + 4) 1.16 ton per seat, 3 car 170 0.73 ton per seat.
2) HST 234 seats, 170 184 seats.
3) My guesstimate assumed both were the same
4) I know and even then the model may not be accurate, somebody else up thread pointed out that the VP 185 15% reduction in fuel consumption proved to be over optimistic. That's why I said someone at Scotrail has the real fuel bills
The real killer is 1 above especially when used on what is basically a semi fast service with frequent stops once away from the Central Belt.

 

[BRX]

A 2+4 HST weighs something like 270T.
A 3 car 170 weighs something like 135T.
So we can agree that the HST needs to shift twice as much weight.
If we assume that both are equally efficient in turning fuel into energy, then even if we also assume that nearly all the energy is used in overcoming inertia, or hauling up grades, I don't see how it's possible to end up at a guesstimate greater than 2x consumption.

 

[hwl]

A 2+4 HST weighs something like 270T.
A 3 car 170 weighs something like 135T.
So we can agree that the HST needs to shift twice as much weight.
If we assume that both are equally efficient in turning fuel into energy, then even if we also assume that nearly all the energy is used in overcoming inertia, or hauling up grades, I don't see how it's possible to end up at a guesstimate greater than 2x consumption.

Hydraulic transmission (or rather the torque converters) are very inefficient at low speeds but the HST traction electrics are pretty poor compared to modern gear efficiency wise.
Aerodynamics are a big part of the physics picture especially above 50mph.

Worth also bearing in mind that the MTU HST engines are significantly derated a the full power setting.

Rail engines spend most of their time at "idle" hence worrying about fuel consumption at full power is only a small part of the picture.

 

[paul1609]

Hydraulic transmission (or rather the torque converters) are very inefficient at low speeds but the HST traction electrics are pretty poor compared to modern gear efficiency wise.
Aerodynamics are a big part of the physics picture especially above 50mph.

Worth also bearing in mind that the MTU HST engines are significantly derated a the full power setting.

Rail engines spend most of their time at "idle" hence worrying about fuel consumption at full power is only a small part of the picture.

Don't the ZF gear boxes on the 170s lock up at about 45 mph?

The engine capacity of a HST engine is 76 litres so 152 for a 2 + 4, the engine capacity of a 170 engine is 13 litres so 39 litres for a 3 car unit. It's a no brainer which is going to be more economical across the whole power range.

 

[43096]

Don't the ZF gear boxes on the 170s lock up at about 45 mph?

The engine capacity of a HST engine is 76 litres so 152 for a 2 + 4, the engine capacity of a 170 engine is 13 litres so 39 litres for a 3 car unit. It's a no brainer which is going to be more economical across the whole power range.

The Haynes Manual quotes the MTU 4000 as being 65 litres.

 

[Domh245]

The Haynes Manual quotes the MTU 4000 as being 65 litres.

I can only assume they've averaged the 12V and 16V versions to arrive at that. The 4000 series have a displacement of 4.77l/cylinder so the 16 cylinder variant in a HST comes in at 76.3l - the 12 cylinder variant comes in at 57.2

 

[hwl]

The Haynes Manual quotes the MTU 4000 as being 65 litres.

MTU say 76.3L ...

I've just done the calculation manually and get 76.265L

 

[hwl]

Don't the ZF gear boxes on the 170s lock up at about 45 mph?

The engine capacity of a HST engine is 76 litres so 152 for a 2 + 4, the engine capacity of a 170 engine is 13 litres so 39 litres for a 3 car unit. It's a no brainer which is going to be more economical across the whole power range.

170 gear boxes transition to fluid coupling between 57 and 64mph (notch 2 / 7 with the others in between). I think you are thinking of the older 75mph max sprinters for ~45mph transition speed.

 

[hexagon789]

170 gear boxes transition to fluid coupling between 57 and 64mph (notch 2 / 7 with the others in between). I think you are thinking of the older 75mph max sprinters for ~45mph transition speed.

I always thought it was about 66-70mph rather than 57 to 64, hence the really sluggish acceleration until about 65/70mph.

 

[notadriver]

Class 170s have got to be the slowest accelerating ‘modern’ British DMU constructed. Despite their engine output of 422 bhp per vehicle. They take about 114 seconds to reach 60 mph a figure a good pacer can almost match. A 2+8 hst is far quicker never mind these shortened 2+4 rockets.

 

[hexagon789]

Class 170s have got to be the slowest accelerating ‘modern’ British DMU constructed. Despite their engine output of 422 bhp per vehicle. They take about 114 seconds to reach 60 mph a figure a good pacer can almost match. A 2+8 hst is far quicker never mind these shortened 2+4 rockets.

From data I've posted before:

0-100mph:

Class 170 - 4.5mins
2+9 HST - 4.25 mins
2+8 HST - 3.75 mins
2+7 HST - 3.25 mins
2+4 HST - 2.5 mins

(All approximate averages)

 

[notadriver]

Sorry I highly doubt that a 170 can reach 100 mph in 4.5 minutes

 

[hexagon789]

Sorry I highly doubt that a 170 can reach 100 mph in 4.5 minutes

Eversholt themselves says 400 seconds (6 mins 40), but I was previously informed that was incorrect. In which case, is 6m40 more likely then?

 

[notadriver]

Eversholt themselves says 400 seconds (6 mins 40), but I was previously informed that was incorrect. In which case, is 6m40 more likely then?

there was meant to be a laughy face at the end of my last post but it failed now a 172 would probably get closer to that figure despite only being slightly more powerful.

 

[hexagon789]

there was meant to be a laughy face at the end of my last post but it failed now a 172 would probably get closer to that figure despite only being slightly more powerful.

Well despite having travelled on 170s on the E&G for years, I honestly couldn't say whether the 4.5 or 6.67 minute figure is correct, simply that they always seem sluggish at lower speeds.

The Highland Chieftain by comparison (of course a 2+9 HST so not exactly comparable to ScotRail's ones) always seemed to pick-up speed more quickly, and the HSTs even at full length are much better at hill climbing.

 

[PG]

Sorry I highly doubt that a 170 can reach 100 mph in 4.5 minutes

unless ECS downhill with a hefty tailwind maybe

 

[43066]

unless ECS downhill with a hefty tailwind maybe

Especially if it’s the driver’s train home.

 

[dgl]

unless ECS downhill with a hefty tailwind maybe

Would it even do that if you pushed one of a very high cliff

 

[paul1609]

What always surprises me is how sprightly the 168s feel considering they are basically the same as a 170. The speed through Ruislip on the down services is particularly impressive. I suspect the answer is that Chiltern is using the trains on services that the actual engine /gearbox/ final drive ratio is designed for rather than what are basically regional stopping services.

 

[Bald Rick]

What always surprises me is how sprightly the 168s feel considering they are basically the same as a 170. The speed through Ruislip on the down services is particularly impressive. I suspect the answer is that Chiltern is using the trains on services that the actual engine /gearbox/ final drive ratio is designed for rather than what are basically regional stopping services.

It helps that it's noticeably downhill on the down to Ruislip.

 

[hexagon789]

What always surprises me is how sprightly the 168s feel considering they are basically the same as a 170. The speed through Ruislip on the down services is particularly impressive. I suspect the answer is that Chiltern is using the trains on services that the actual engine /gearbox/ final drive ratio is designed for rather than what are basically regional stopping services.

I don't think the distances between stops are that significantly different from some services ScotRail used them on.

 

[Railperf]

Sorry I highly doubt that a 170 can reach 100 mph in 4.5 minutes

I recorded a 170 from Linlithgow heading towards Glasgow -uphil 1 in 682 for 3.5 miles and downhill 1 in 960 thereafter.
0 to 60mph in 1 min 45 secs and 0 to 100mph in 5 mins 30 sec.
Conversely i found a file of Anglia's last 170 doing 0 to 60mph in 1min55 sec and 0 to 98mph in 6 min 10 secs (7 miles) from a start at Stowmarket towards Ipswich. Downhill most of the way at varying rates, some level stretches and nothing steeper than a short stretch of 1 in 337, almost 2 miles at 1 in 911, and almost 2 miles of level track in amongst all of that.

 

[hexagon789]

I recorded a 170 from Linlithgow heading towards Glasgow -uphil 1 in 682 for 3.5 miles and downhill 1 in 960 thereafter.
0 to 60mph in 1 min 45 secs and 0 to 100mph in 5 mins 30 sec.

That's in the middle of the data I posted. It seems reasonable, they certainly don't get up to speed that quick either way!

 

[Railperf]

That's in the middle of the data I posted. It seems reasonable, they certainly don't get up to speed that quick either way!

So there are a number of conclusions to draw here!
A Class 170 needs to spend 230% of the time an HST does to reach 100mph 6 mins v 2.5 min
The HST MTU engine consumption figure was 944 l/hr based on 5364hp setting
Assuming a reduction in power to 4500hp reduces the fuel consumption by a similar percentage - the fuel consumption could drop to appx 790 l/hr

In that case - The 170 could be using appx 22 litres to reach 100mph in apps 6 to 7 miles.
HST on full power for 2.5 mins (and 2.5 miles) could be using appx 32 litres to accelerate to 100mph. The HST reduces to idle for the remaining 4.5 miles and would be using whatever fuel is needed to idle for that time. Could be several litres.
At that point - the following characteristics determine how much fuel is needed to maintain line speed - rolling resistance, kinetic energy - air resistance due to aerodynamics etc.
The HST has greater kinetic energy as it weighs almost twice the amount. But is also likely has greater rolling resistance - more vehicles and wheelsets. And although the pointed nose of the HST may look aerodynamic, there is a greater area of bodyside, underside and roof area dragging through the air. So I am inclined to believe (I am not an engineer) that these factors may well equal out - between the two trains - if not favour the 170.
I'm imaging the cost of cleaning and maintaining the HST is higher - more vehicles - two power cars and four coaches vs a three car DMU. Probably parts for the HST MTU engines are dearer than the smaller more ubiquitous 170 engines.
The HST will consumer more brake pads due to the greater train braking weight, and there are more brake pads/discs and wheel sets to change too.
The HST's are not 'green' machines by any stretch of the imagination!
But taking into account leasing costs vs the cost of leasing a brand new train - say 4-car Class 755's - is the HST cheaper? Reliability has to be taken into account too. How many more HST failures (causing lateness delay or cancellation) will cost the TOC even more money?
Which proves fuel economy is not the only consideration. But i think we can see the HST is a greater gas guzzler than a 170.

 

[hexagon789]

But i think we can see the HST is a greater gas guzzler than a 170.

Definitely, I never intended to question that it was only the supposed difference between 170s and HSTs that I was questioning.

 

[Railperf]

Definitely, I never intended to question that it was only the supposed difference between 170s and HSTs that I was questioning.

I guess that they hope to recoup any increased running costs by attracting more bums on seats.
That is achieved in 2 ways - having a frequent and reliable service. Offering journey times and ticket prices that compete with the private car.

 

[hwl]

So there are a number of conclusions to draw here!
A Class 170 needs to spend 230% of the time an HST does to reach 100mph 6 mins v 2.5 min
The HST MTU engine consumption figure was 944 l/hr based on 5364hp setting
Assuming a reduction in power to 4500hp reduces the fuel consumption by a similar percentage - the fuel consumption could drop to appx 790 l/hr

In that case - The 170 could be using appx 22 litres to reach 100mph in apps 6 to 7 miles.
HST on full power for 2.5 mins (and 2.5 miles) could be using appx 32 litres to accelerate to 100mph. The HST reduces to idle for the remaining 4.5 miles and would be using whatever fuel is needed to idle for that time. Could be several litres.
At that point - the following characteristics determine how much fuel is needed to maintain line speed - rolling resistance, kinetic energy - air resistance due to aerodynamics etc.
The HST has greater kinetic energy as it weighs almost twice the amount. But is also likely has greater rolling resistance - more vehicles and wheelsets. And although the pointed nose of the HST may look aerodynamic, there is a greater area of bodyside, underside and roof area dragging through the air. So I am inclined to believe (I am not an engineer) that these factors may well equal out - between the two trains - if not favour the 170.
I'm imaging the cost of cleaning and maintaining the HST is higher - more vehicles - two power cars and four coaches vs a three car DMU. Probably parts for the HST MTU engines are dearer than the smaller more ubiquitous 170 engines.
The HST will consumer more brake pads due to the greater train braking weight, and there are more brake pads/discs and wheel sets to change too.
The HST's are not 'green' machines by any stretch of the imagination!
But taking into account leasing costs vs the cost of leasing a brand new train - say 4-car Class 755's - is the HST cheaper? Reliability has to be taken into account too. How many more HST failures (causing lateness delay or cancellation) will cost the TOC even more money?
Which proves fuel economy is not the only consideration. But i think we can see the HST is a greater gas guzzler than a 170.

One of the issues / questions TS had was around the level of suppressed demand because of the many existing short services and the HST gave the option to increase seating and examine interior options before further electrification and going for bi-modes in the future.

The HSTs allowed an increase in seats with the cheap and easy potential to add more

 

[Railperf]

One of the issues / questions TS had was around the level of suppressed demand because of the many existing short services and the HST gave the option to increase seating and examine interior options before further electrification and going for bi-modes in the future.

The HSTs allowed an increase in seats with the cheap and easy potential to add more

Very true. Pretty easy to add in an extra vehicle or two - as long as they procure enough before the rest go for scrap.