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The Way It Is/ Searching for efficiency au Petit Le Mans

by Gordon Kirby
The Petit Le Mans takes place over 1,000 kilometers or 10-hours at Road Atlanta next weekend. It's the American Le Mans Series second-biggest event of the year, behind only the season-opening Sebring 12-hour classic, and this year's race is sure to witness a fierce battle. Peugeot is bringing over one of its 908 closed coupe LMP1 cars to try to challenge for overall victory while Indy car stars Dario Franchitti, Scott Dixon, Tony Kanaan, Marco Andretti, Helio Castroneves and Ryan Briscoe are also in the field aboard P2 cars. Franchitti, Dixon, Kanaan and Andretti are in Acuras while Castroneves and Briscoe will share a third Penske Porsche.

This year's P1 championship has already been wrapped-up by Audi drivers Lucas Luhr and Marco Werner but the P2 title fight is wide-open with two rounds remaining--the Petit Le Mans and Laguna Seca two weeks later. The P2 battle is between Romain Dumas and Timo Bernhard in one of Penske's Porsche RS Spyders and Scott Sharp and David Brabham in Duncan Dayton's Highcroft Acura ARX-01b. Going into Road Atlanta, Dumas/Bernhard lead Sharp/Brabham by four points in the drivers championship, but the opposite is true in the manufacturers championship with Acura leading Porsche by four points.

Making its debut at this year's Petit Le Mans is the ALMS's 'Green Challenge', a new efficiency-based category expected to feature cars other than the front-running P1 and P2 prototypes. It will be interesting to watch the 'Green Challenge' unfold and see how much interest it attracts from competitors, fans and media.

Fuel mileage and efficiency is important in all types of racing, of course, but it's particularly critical in long-distance sports car racing. It's sure to be a factor at Road Atlanta and the Penske/Porsche combine hopes good fuel mileage from Porsche's new direct injection engine will help them defeat the Acura troops. The new engine first raced this summer in Penske's Porsches and will probably be raced next year by most Porsche P2 customers in the United States and Europe.

This is the third and final year in Penske's contract with Porsche and discussions are currently taking place about extending the agreement. If that doesn't happen, the RS Spyders will continue to race with Porsche customer teams like Rob Dyson's operation. Nevertheless, it's particularly important for both Penske and Porsche to win the P2 championship for the second year in a row, hence the addition of a third car at Road Atlanta for Castroneves and Briscoe.

To help in fending off Acura's fleet of P2 cars, Porsche developed its new direct injection engine last year and completed the development program this spring so the engine could be raced in the second half the season. Direct injection of the fuel mixture into the cylinder head rather than the intake port is common practice in diesel engines, of course. It's rarely employed in gasoline-burning engines, but over the past ten years Porsche has developed direct injection engines for its road cars, including the current 911 and Cayenne.

Recently, I talked to Porsche engineer Thomas Laudenbach about the development of direct injection for its racing RS Spyders. Dr. Laudenbach is responsible for power train development in Porsche's motorsports department.

"We are already using this technology in a wide range of our road cars," Laudenbach commented. "The first thing we did when we decided to pursue this technology was we went to the road car guys and asked them, 'Can you tell us what this technology is about?' It was a very close partnership. We wouldn't have been able to do it in that period of time without them. But at the same time I think we were really able to help them in the end, in a certain range. But nevertheless, we did help them.

"We worked very closely with the road car development guys. The same guys did the development for the motor sport program that did the road car development. At the beginning, we tried to get as much information from the road car program as we could. We went very deep into a small range because that's what racing demands. We went into it very, very deep, and we found we could give good information and feedback to the road car guys."

The direct injection engine is based on the port injection engine Porsche raced in 2006, '07 and the first half of this year.

"We had a great year in the ALMS in 2007 and we won the LMP2 class at Le Mans this year with this engine," Laudenbach noted. "So we had a good engine and to make the new engine better was a difficult thing."

Porsche's racing department started thinking about direct injection in 2004.

"Obviously, Audi has shown it works with a turbocharged diesel engine," Laudenbach said. "But at that time many people weren't sure that it was really an advantage for a naturally-aspirated, high-revving, gasoline engine.

"In our pre-development studies the interesting thing we found was that we had to do a new approach to the development. We found the experience we had from the port fuel injection engine wouldn't get us where we wanted to go. The first step took us months, or even years, and that was to build up the method and the calculation to do a direct injection engine."

It wasn't until late last year that Porsche had enough information to determine that such an engine would be a bonus in both power and fuel mileage.

"In 2007 we came to the point where we said, yes, we are convinced that if we do this it should help us," Laudenbach remarked. "By that point we had the LMP2 program running and we thought it should really give us an advantage compared to the port injection engine."

Serious development of the P2 direct injection engine started in November of '07.

"By then we were really under time pressure because the goal was to race the engine in the middle of the 2008 season. We always had in mind as a goal to debut the engine after the Le Mans break."

The engine was first raced at Lime Rock in July and Laudenbach stressed that improving fuel mileage was the primary goal.

"The big point is not to increase power," he observed. "We are talking about long-distance racing where you sometimes win with higher efficiency and less fuel consumption. But in the end we were able to increase the power really significantly by around five percent, which is a huge number for such a step. At the same time the specific fuel consumption went down five percent, which means we gained a lot of power and didn't use more fuel. We even used a little bit less fuel.

"So if we want to, we don't have to use the power. We just use the fuel mileage. It really was a development for efficiency. We wanted to show that even with a rather high-revving, naturally-aspirated engine, it made sense to do it."

Laudenbach explained the challenges of introducing the fuel charge directly into the cylinder head of a gasoline-burning racing engine.

"Imagine an engine revving 11,000 rpm," he related. "You have nearly eleven milliseconds in the port fuel injection engine to inject the fuel for one cycle. For the direct injection engine you have about 1.5 milliseconds to inject the fuel. So you've got to be extremely accurate. You can only inject the fuel when the inlet valve is open because you need the charge motion to make it work. If you start too early, the exhaust valve is still open and then you take the risk that fuel is taken out the exhaust which, obviously, you don't want.

"If you start too early, you will lose efficiency straight away. You are restricted by the optimum ignition and you have to get the mixture preparation to be homogeneous in a very short time. So you have to be extremely accurate with everything. You are more sensitive on the fuel temperature. You really have to calibrate everything."

Laudenbach says there was plenty to learn in a short space of time.

"It wasn't easy. For us, it was unknown territory. We are still learning with it and many things came up that we never thought about. It's a very sensitive engine. It's far more sensitive than injecting the fuel into the port.

"We have a perfect comparison to the 088-spec port fuel injection engine," Laudenbach added. "It's basically the same engine with direct injection and what we see is we are far more sensitive on the whole injection process--the injection timing, the injectors themselves--everything, and on the fuel quality, which is an important point. It's also far more sensitive on port design and on cleanliness inside the combustion chamber."

Most of the changes are restricted to the top end of the engine.

"We tried to keep as many of the old parts as possible because we had the mechanical durability," Laudenbach noted. "So we didn't change the crankshaft or the rods. But we had to do some internal work to the cylinder heads, and to the pistons and cam profile. We changed the inlet cam profile and we changed the exhaust valves, but we stayed with the same springs and the same system. The top end from the cylinder head gasket upward, including the pistons, is completely new."

Finding the correct design for the intake port took a lot of time and effort.

"The big difference is that in a port fuel injection engine the main thing you try to improve is your flow coefficiency because you save energy for exchanging the gas, and it's waste energy. With the direct injection engine you have to do that, but at the same time, you need a certain charge motion in the combustion chamber. If you don't have sufficient charge motion, you won't get a proper mixture preparation and get the mixture homogeneous. It will run, but it won't be better than the port injection engine. It will be worse.

"It's easy to put a hole in the combustion chamber and put the injector in there. It will run, but to gain a significant advantage against the same port injection engine, that's not too easy. That is a difficult thing to achieve."

Laudenbach confirmed that computer-aided simulation studies formed a big part of the early work on Porsche's direct injection engine.

"A core point of the development work was the simulation work," Laudenbach related. "We did a lot of simulation of all the internal things that happen--flow simulation up to combustion, the mixture preparation and how it's distributed inside the cylinder just before ignition. That is something you don't do so intensively for a port injection engine. You do it sometimes, but it's far away from what we did for the direct injection engine. Internal engine simulation was a clear, core point."

Laudenbach described the process of developing the engine as a three-step program.

"First, we discovered that new development rules were required. We couldn't do it just with the experience and calculation methods we had used with the port fuel injection engine. We found that out very quickly, especially in describing what's happening inside the cylinder.

"In the port injection engine you always get nearly homogeneous mixture and don't worry too much about what happens there. But with the direct injection system we realized everything happens inside the combustion chamber. We had to build much better knowledge of what happens and how we can influence it.

"First of all, we had to build up the tools--the computer models and the mathematics behind it. We got wonderful nine-color pictures out of it and we said that's nice, but is it good? For example, at the point where you start ignition, there's X percent of liquid fuel. We asked, is that good, or bad?

"So we really had to build up our experience and that was always accompanied by dyno tests. We calculated it, and then tried it on the dyno and built up our knowledge. That work wasn't done with the P2 engine. That was all part of the pre-development work.

"The next step was, where are the target values? What does the 'tumble' of the fuel mixture inside the combustion chamber look like? We had to build target areas for each value of where we had to go to."

The third and final step was the most difficult.

"After knowing where we wanted to go the question now was, how do we get there?" Laudenbach asked. "What does the port design and piston design look like? That took us some time. But when we did arrive there, that was when we said, yes, this is an advantage.

"We had times that we said it's never going to work," he added. "To be honest, we didn't have a straight route. But when you introduce new technology, that's how it is."

With the Acura teams making steady progress this year thanks to an intensive development program from Honda Performance Development and Wirth Research, the new direct injection engine may prove a key component in Porsche retaining its LMP2 championship title.

"It was the right time to bring it to the track because we see how hard the competition is from Acura," Laudenbach remarked. "They're doing a great job and putting a big effort into the whole thing. But I'm convinced that we have a clear advantage on fuel mileage."

Laudenbach says he doesn't believe anyone other than a major manufacturer will be able to successfully develop a direct port injection, gasoline-burning racing engine.

"To be fair, I think this technology, as far as a naturally-aspirated, high-revving engine, would be very difficult for a private, small company to design because you've got to build-up your tools at the first stage of pre-development. That will be difficult for companies like AER or Judd.

"It's a very sophisticated thing to develop," Laudenbach added. "It's difficult, but very interesting for the engineers because we learned a lot. And the most important thing is that, yes, we get efficiency from it. I think it's a step in the right direction. It's just one small step. We need far more steps like this, but it's definitely a good step. That's one of the reasons we said we wanted to bring the direct injection engine into the LMP2 car."

Finally, Laudenbach says developing this engine has been one of the best examples he's witnessed of Porsche's road car and racing divisions working together.

"The car companies like to talk about the synergies between road cars and racing, and sometimes they talk more than it may really be worth," Laudenbach observed. "But in this case, I really have to say it was a great partnership. They were able to help us and we could help them. It really went together and that was really a nice thing. It was very interesting and sometimes difficult, but in the end we are really proud of the result."

At Road Atlanta next weekend and Laguna Seca two weeks later, we'll see if Porsche's direct injection engine can help the Penske/Porsche team defend its P2 championship.

Auto Racing ~ Gordon Kirby
Copyright 2008 ~ All Rights Reserved

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