Re: That 'efficiency' thing again

About 20 months ago there was a long thread on this group regarding
efficiency, which was prompted by an article in the "Observer"
regarding future high speed lines.

I compared the energy consumption of an HST, IC225 running on the
upgraded WCML against a new LGV using a TGV Atlantique clone.

I also compared the energy consumption of a Boeing 737-400 flying from
Heathrow to Glasgow and a car journey using an Audi A4 2.5TDI Avant
(my own car, using the official 40.4 MPG fuel consumption figures)
also from Heathrow to the centre of Glasgow.

I thought it would be worthwhile repeating what I stated then:

I have made some amendments to the basis for the calculations as
peeople have kindly pointed out that the B737-200 is a pessimistic
aircraft to use for comparison purposes and quite dirty. Due to the
time and data available, I have used the B737-400 instead, for which
I
had data to hand.


The basics of this exercise if to establish the energy per seat it
takes for the following modes of transport to complete a journey
of 660km:


An IC125 diesel set - Valenta powered (VP185 and MTU data not
available
to me)
An IC225 set - electrically powered
Both were assumed to have 450 seats and were taken on a 5 hour
diagram
of the WCML for comparison purposes. This line I have modelled to use
132kV fed traction substations to give an idea of the efficiency
which
will be generally experienced in the UK. (The WCML will eventually be
fed from only nine 400kV substations as from 2009)


A 337 seat TGV Atlantique on a typical LGV track with up to 1:40
gradients over a 660km diagram, taking 2 hours 45 minutes with a
maximum speed of 300km/h. The feeding to the traction substations was
assumed to be at 400kV throughout


An Audi A4 Avant 2.5 TDi diesel car with 4 passengers (I can advise
that getting five in is possible, but uncomfortable over such a
journey
length).


The model takes into account the following:


Energy losses from when fuel is landed onto the UK shoreline at a
refinery or a gas compressor station, including refining and
distribution by pipeline (aircraft) or by road lorry (IC125 and car),
or for gas; the losses included in compressor stations. The basic
model
assumes gas fired generation, but the results were calculated again
on
the basis of nuclear generation.


Thermal efficiency of gas turbine at power station, or diesel
engine(s)
in IC125 and car.


Electrical losses for the grid and distribution systems and within
the
25kV OLE itself.


The conversion efficiency of the drive for each type of train and the
car.


For each train, it is assumed that the journey is in spring or autumn
and thus the hotel losses are moderate, but are included. The effect
of
using maximum hotel loads is genrally insignificant in terms of the
overall ranking.


And the results are:


B737-400: 874MJ/seat
IC125: 575MJ /seat
IC225: 455MJ/seat (625MJ if nuclear generation is assumed)
TGV - A: 455MJ/seat* (625 MJ if nuclear generation is assumed)
Audi car: 490MJ/seat


* This result surprised me and looked suspiciously like the IC225. So
I
double checked the modelling. The total energy consumption for the
IC225 set was 56MWHr (inclusive of all losses), whilst that of the
TGV
-A was 47MWHr (inclusive of all losses). Factor that by the seating
available on each set and the result is the same!


The purposes of this modelling exercise were originally intended to
sense check the paper by Prof Roger Kemp, published in 2004 and were
further developed as a result of this thread to include all losses
from
the fuel arriving at our shores. The accuracy of some of the
assumptions on refinery efficiency, gas compressor efficiency and
losses involved by fuel distribution are unvalidated, but seem to
make
broad sense. As these losses are small when compared to say the drive
losses on an IC125, tweaking them even by an order of magnitude will
not serously affect the outcome.


The aircraft energy usage assumed that the plane was loaded to 75% of
maximum take off weight and spent 25% of its time in LTO operations,
with no headwinds and minimum allowable fuel reserves. As this was
the
first time trying to model an aircraft in any detail (as opposed to a
simple energy per flight type calculation), what interested me was
how
sensitive the results were to some minor tweaks to the "flightplan" A
delay of say five minutes in reaching the cruising altitude of FL30
(30,000') caused the energy consumption to shoot upwards to over
1000MJ/seat. Likewise headwinds. If the plane is operated with only
passengers, no cargo and no hold baggage over an optimal route with
no
ATC delays, the energy used recedes to about 700MJ per seat.


Contrasting this to the railway operations, the amount of energy used
whether the train is full of passengers or not makes less difference
to
the whole energy consumed because payload is a small percentage of
all
up weight, whereas it is much larger with an aircraft.


Overall an interesting exercise. Calcs are underway for an Airbus
A320
and Dr Who's Tardis for the next edition.

Ray
.

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