After 15 years of dominating Europe’s passenger-vehicle market, the compression-ignition engine is being challenged. A new generation of downsized-and-boosted spark-ignition engines is increasingly capturing share, causing diesel’s market penetration to flatten out and even decline in some countries.
Nowhere is the development of super-efficient gas engines more of a priority than at VW Group, observed Dr. Hermann Middendorf, head of development for the group’s EA111 engine family – the smallest displacement gasoline engines used in VW, Audi, SEAT, and Skoda vehicles.
“For sure we at Volkswagen have put a strong new focus on gasoline-engine development,” Middendorf told AEI during a late 2009 interview in Germany. He said three factors are behind VW’s shift in strategy. First, the increase in diesel fuel’s retail price (due to tax legislation in most countries) has diminished its price advantage vs. gasoline. Pump prices of the two fuels are close to parity.
The second factor is VW’s spark-ignition R&D is paying off. Middendorf’s colleagues on the gas-engine side are delivering products with greater output, comfort and smoothness, and increasingly lower fuel consumption.
“This combination is making our new TSI (turbocharged spark-ignition) gasoline engines very successful, and many diesel customers have already changed over to the gas engines,” Middendorf said.
The third factor is the gasoline engine’s inherent cost advantage over a comparable diesel, even as engineers add intercooled turbochargers and sophisticated valve-control hardware.
“Cost of the gasoline engine is a big point in our engine strategy,” he noted. “During the last decade we were very successful with our TDI engines. We were the market leader everywhere. But it was a high-risk strategy, due to the higher emission standards we have to fulfill in all our markets.
“We have to put more, very expensive technologies, including aftertreatment, into the diesel engines in order to pass the tighter standards,” he explained. “So to rely only on the diesel technology was a very high-risk business case for us.”
He said VW’s decision to halt development of a simple lean-NOx trap aftertreatment system for the Tiguan 2.0-L TDI intended for U.S. sale was “quite emotional” for the engineers involved. The vehicle was in the process of EPA certification when the program was stopped.
“To achieve the high sales numbers, you must have no doubt about the effectiveness of the emission-control system,” he explained. “We have to be on the safe side and have no doubts about the technology.”
Searching for cheap solutions
Middendorf characterized VW management’s decision to significantly increase gasoline-engine R&D as a “big step” for the company. He stressed that while VW engineers are working to keep the diesel cost-effective while further improving its efficiency, the fundamentals of the spark-ignition engine as it applies to future vehicles are undeniable.
“It’s a much cheaper engine to produce. Its structure is simpler. It has a lot less material and less weight. Putting these new gasoline engines into our cars, we come very close to the fuel efficiency of the diesel, but with much lower costs,” he said.
Middendorf said he doesn’t expect VW’s advanced gasoline engines will have to add in-cylinder pressure sensing capabilities going forward, in order to meet more stringent emission regulations.
“Due to the quite low combustion-conversion ratio, we have no problem with NOx emissions as diesels have,” he explained. “We are sensing combustion using the [crankshaft] speed-sensor signal to see what the engine is doing and the torque that is delivered by the combustion of each cylinder. It’s an indirect system but it works very cost-effectively and robustly.”
He added that his teams “have to keep our technology on the low-cost side, otherwise we would have costs like a diesel. We must maintain a significantly lower price level on the petrol engines. We’re always looking for cheap solutions.”
Cost is also important as VW expands its plans for hybrid-electric vehicles, said Middendorf. “Diesel hybrids present a very difficult business case, with two costly systems [the diesel engine and battery pack] to deal with.”
Middendorf acknowledged the CO2-emissions advantage of diesel engines, but said he is extremely encourgaged by VW’s gasoline-engine testing on ethanol fuels. “As energy and fuels become more expensive, it makes sense to refine these fuels to burn at the highest possible efficiency. Ethanol in gasoline engines allows us to run high compression ratios due to the high knock-stability of the fuel. So we can reduce CO2 emissions a lot.”
VW is using a “two-track” development approach using gasoline and diesel engines in its plan to tackle the next round of European and U.S. emissions regulations expected this decade, said Middendorf. He has spent his entire 21-year career in powertrain engineering at VW, following mechanical-engineering studies at Hannover University.
On the advanced-combustion front, VW has been in the vanguard of developing homogeneous-charge compression-ignition (HCCI) technology, which promises significant increases in gasoline-engine fuel efficiency. When asked if the program has moved from R&D into a production-development phase, Middendorf paused before answering carefully.
“The technology is still under investigation,” he replied. “We have not decided on start-of-production for HCCI. We’re working continuously to improve the combustion process. When we make the gasoline engine combustion process more like a diesel’s, then we have a NOx emissions challenge more like the diesel.
“Therefore we have to find a new way, also with this HCCI combustion process, to keep the advantages of the gasoline engine and not get [emissions] problems like on the diesel side.” He said while VW’s R&D engineers are investigating specific fuels that are most amenable to homogeneous combustion, the big challenge is developing the process so it can be used in global vehicle applications – “for use in places where there is not widespread availability of fuel types.”
Similar to the current HCCI development paths of GM and Mercedes, VW’s strategy is to use spark-ignition modes to handle high-load operation as well as at idle, with HCCI mode occurring between the two.
“Yes, we use HCCI for the ‘main operation’ area. It’s easier to fit with all the restrictions we have,” Middendorf noted. “Particularly with hybrid cars, it gives more freedom to make the engine run in the ‘sweet spot’ of that technology. So we have to perhaps rethink our use of this [HCCI] technology.”
Will VW introduce a production HCCI engine in this decade, as some major engine-systems suppliers have indicated? “We’re always improving our engines’ combustion and investigating what is the next big step,” said Middendorf with a laugh. “It will be in combination with electrification. That will be the next task.”
He said VW currently has high-performance TSI and diesel engines “running effectively on their own and in combination with electrification.”