Interview with Dave Morrison, Ricardo Motorsport, on the
Ricardo / Engine Developments Diesel Le Mans Engine Project
of racing a diesel engine at Le Mans, with the aim of winning the
race, first arose during the 2002 Autosport International show at
the UK’s National Exhibition Centre. There, Ricardo Motorsport
was approached by a team interested in such a project - but at that
time it was unclear what the rules would be for a diesel engine.
After Ricardo had discussions with the ACO about diesel engines,
regulations for them were published at the end of 2002. Initially
Ricardo considered three options: firstly its own design based on
a 5-litre V10, then converting an existing production engine, before
finally choosing to convert an existing race engine. Alan
Lis asked Dave Morrison, Ricardo Motorsport Business Operations
Manager, about the progress made so far and the future prospects
for the project.
did you reject the idea of building your own engine?
“Although it was a conventional diesel, it would have had
very high cylinder pressures and high torque, something like 1300
Nm at 2500rpm. That would have been a real challenge for the transmission
and the engine itself would have been on the heavy side.”
you decide that converting an existing race engine was the way forward?
“In January 2003, when we started talking with Engine Developments
Ltd about the possibility of converting their V10 engine to run
on diesel fuel. We then started doing some theoretical modeling
that showed that there were some possibilities. It’s a technically
fascinating project and would be the first truly race optimised
diesel engine. The diesels that are racing now are just conversions
of road engines. This would throw all that out the window: we can
forget about extreme durability, because the engine only has to
last 30 hours so we can make a relatively lightweight structure.
The bottom end of the Judd V10, with its bed-plate construction,
is quite rigid, so we reckon it’s strong enough to take quite
point in time does an engine exist other than as a computer model?
“We’ve built a four-cylinder mule engine based on one
bank of a Judd V8, to demonstrate the principle. That engine already
has a very narrow valve angle, which suits a diesel application
quite well. We designed the combustion chamber and Judd made it
as a mule engine and, we very much hope, that will lead ultimately
to a diesel V10, but the whole project depends on funding.”
ratio would be required?
“Quite a low one by diesel standards. You couldn’t get
away with the compression ratio we would use for racing on a road
engine because of the cold start requirement. On a race engine you
want to run as a low a compression ratio as you can get away with,
to restrict the cylinder pressures.”
of torque output is possible?
“With the engine we designed about three years ago, what I
would call a pure racing diesel in terms of very high cylinder pressures,
we were looking at very high torques, around 1200Nm. The new engine
would generate a lot less torque although it would be more than
a comparable turbocharged gasoline LMP900 engine, but not by a lot.
“The torque curve
would have a different shape, because of the different characteristics
of a diesel engine. There would be more torque at the bottom end,
which means that driveability and pulling power out of corners will
be much better than a gasoline engine. We have even been debating
how many gears would be needed in the transmission to take full
advantage of that. If you have a better torque curve shape maybe
you don’t need so many gear changes. Less gear changes means
a little bit of time saved on a lap.”
maximum rpm be?
“Fairly high for a diesel. A current diesel engine for a road
car would make peak power at around 4500rpm, we are targeting a
bit more than that. We’ve run diesels to 6000 before. Our
speed will be high for a diesel engine but not for a gasoline engine.”
you have any projections on how fuel efficient the engine might
“Yes, we obviously done some modelling of this. We’ve
predicted how many extra laps we would get. It’s no secret
that the Audis with the DI engines were getting another 1-2 laps
over the competition at Le Mans in 2003.”
with the smaller ACO air restrictors the Audis were able to do 15
laps on a tank of fuel. Would the diesel engine be able to match
“It would be able to do more laps, perhaps 1-2 more. The initial
calculations that we have done suggest that it’s enough of
an increase to make it worthwhile. A racing diesel engine would
be up against the same sort of problems as a racing gasoline engine.
The principle that a diesel engine would be more reliable is not
as valid in a racing application.”
changes than a new cylinder head design would be needed for a diesel
“You would need new pistons for the changed compression ratio
and a slightly taller block to accommodate them, because a modern
day gasoline piston has very little skirt provision and a shallow
crown, so there would not be enough room for a bowl. The pistons
would have to be 20-25mm taller to make room for the bowl in the
crown and that means a heavier piston. Some of the weight disadvantage
could be overcome using compromises that have found their way into
other race engines, such as two piston rings instead of the usual
“The aim would
be to keep as much of the original engine design as possible. Pretty
much all of the new parts would be at the top end of the engine.
It’s the same process as converting a road engine from petrol
to diesel. You might change the specification and size of the main
bearings slightly, but typically you would try not to change the
bottom end at all.
“The location of
the injector would also be different because in the ideal diesel
combustion chamber you want the injector positioned centrally and
vertically, above a perfectly round bowl in the centre of the piston
crown. That’s sometimes not achievable, but on most road engines,
in most cases, it can be done. In a race engine it may be necessary
to have more of a compromise. Packaging the injector is not easy
because it’s quite a bulky item compared with a spark plug.
Also it would have to withstand a high clamping because of the high
cylinder pressure it would be working under. In an aluminium cylinder
head, as you have on a race engine, the injector would need to be
clamped down pretty firmly. There’s a bit of a design challenge
in that area.”
Is the fuel
feed strategy for a race engine any different to a road engine?
“The basic principle would be the same. You would be injecting
the diesel fuel into air at a very high air:fuel ratio, otherwise
there would be too much smoke. You can’t burn diesel like
you would gasoline. You can’t ignite a homogenous mixture
with a spark for example. If you ran the same air:fuel ratio as
a petrol engine, there would be clouds of black smoke. A diesel
engine typically runs an air:fuel ratio from 20:1 to 40:1.
“The control strategy
for diesel fuel injection on a road car is quite complex. With modern
electronic control and common rail injection, where you have a separate
pump with a pressurised rail, you open the injector electronically
to admit as much fuel as you want. All of the control is electronic
so you can achieve multiple injection, special injection strategies
for cold starting, for high performance, whatever you want. For
racing the control strategy would actually be a bit easier, but
not quite so challenging.”
a racing diesel engine not have been possible before electronic
“It would have needed a different approach. Boost management
is the biggest challenge, to ensure that you’re getting the
right amount of air into the engine.”
you addressing the boost issue?
“Ricardo has done a lot of research on two-stage boosting
for research purposes in road engines. You are looking at very high
boost and very high engine performance but it’s complicated
and tends to add weight, so we’d rather not do that for a
race engine. Because we’re operating at relatively low pressures
we think we can probably just use single stage boosting. We’re
talking to turbocharger manufacturers (that we have very close contacts
with) to supply the technology to do that. It doesn’t have
to be that complex.”
weight would a diesel cylinder head and turbocharger system add
to the existing Judd engine?
“That’s a key question. Undoubtedly the diesel engine
would be heavier: a common rail injector is a large and heavy steel
item that has to withstand pressures of up to 1600 bar, so its has
to be strong and heavy. Then you have ten of them sitting on top
of the engine, not in an ideal position. We haven’t done the
calculations yet, but I don’t anticipate it adding up to a
big weight penalty. Not as a big a penalty as converting an existing
road going V10 (one that’s designed for a service life of
a quarter of a million miles) to a race engine.
“Of course racing
cars are typically built underweight and ballasted up to the minimum
limit. I would think that the additional weight of the diesel engine
could be allowed for in reduced ballast.
“It’s a fascinating
project I really hope we can do it….”