A Tale of Two Engines
One is a gasoline-powered engine that resembles a diesel in some ways. The other is a diesel with the NVH characteristics of a gasoline-powered engine. Here's an introduction...
#Mitsubishi #BMW #Jaguar
The issue of fuel efficiency is a key concern among auto makers—again. A couple of alternatives were recently introduced in North America, one by a Japanese auto maker, Mitsubishi Motors Corp. (Tokyo), and the other by a European diesel company, VarietyPerkins (Peterborough, England), through Perkins Technology, its engineering consultancy. The Mitsubishi approach is for a gasoline-powered engine. Perkins' is, of course, diesel. Mitsubishi, as a car maker, has a platform to install its engine. Perkins, which is strictly a supplier, is looking for a vehicle-builder to accommodate its engine.
The Mitsubishi Motors development is the GDI engine—Gasoline Direct Injection. This engine, which is actually in production in Japan, was announced to the U.S. market in February. According to Dr. Hiromitsu Ando, deputy general manager, Engine Research Dept., Mitsubishi Motors, "The in-line, four cylinder, 1,834-cc GDI is an engine engineer's dream. It features 10% more output and torque, faster acceleration, and 35% to 40% better fuel efficiency during idling and varying speed conditions compared to conventional multiport injected engines. In addition, we have been able to control NOx emissions, even while burning a lean fuel-air mixture." However, the numbers that they are able to provide with regard to NOx don't meet the Environmental Protection Agency numbers for the U.S. market for the life of the engine. Ando admits that they are working on the technology so that it will meet the European Phase III regulations, which take effect in the year 2000, and which are similar to the U.S. low emissions vehicle (LEV) standard. So it probably won't be until then that there will be any GDI engines running the streets here.
Direct injection of gasoline, Ando points out, is not a new idea. For example, back in 1893 it was unsuccessfully tested—by a man named Diesel, who went on to other things. Mercedes had a direct injection system in the 1954 300SL. Through the years other auto makers have attempted to make more fuel-efficient direct injection engines, but ran into problems ranging from spark plug fouling to soot emissions.
So what has Mitsubishi done? According to Ando, there are three key aspects of the GDI:
- Upright, straight intake ports. Instead of horizontal ports, which are the conventional orientation, these direct the airflow down on top of the pistons.
- Curved-top pistons. The piston top controls the airflow in the combustion chamber, which goes in a reverse tumble, and the air-fuel mixture. The piston configuration was the result of laser-based in-cylinder observation techniques.
- High-pressure, electromagnetic swirl injectors. They essentially spin and spray that atomized fuel directly into the airflow in the cylinder just prior to ignition. When it hits the curved-top piston it is directed toward the spark plug in what is said to be an optimally stratified form.
The results of this are characterized in one test that was conducted in Japan wherein a Mitsubishi Gallant sedan equipped with a GDI engine traveled 800 miles on a single tank of gas (17 gallons).
The GDI engine was introduced in the Japanese market in August, 1996. Customers could get a Gallant with a GDI engine or a conventional one, and of the vehicles ordered, 97% opted for the GDI. The engine is also available on the Legnum station wagon. Sixty-seven percent of the orders were for GDI versions. In total, some 37,000 GDI engines are on the roads of Japan. Later this year the engine will be made available in Europe on the Mitsubishi Carisma, which will be produced by NedCar.
According to Ando, the cost of a vehicle with GDI is about $300 more than the same car with conventional port injection. Certainly, there must be some additional costs in machining the configuration on top of the pistons. Also, the high-pressure swirl injector is different than what's ordinarily available. And there is also a recently developed lean-NOx catalyst in use.
It is interesting to note that even though the intake ports are vertical, there was not a packaging problem with regard to getting the GDI engine into existing models. The GDI is just 20 mm taller than a conventional engine. As Mitsubishi already had an engine with variable valve timing that is also 20 mm taller, the space was available under the hood.
Diesels are not status quo in the U.S. Yet, according to Steve A. Faulkner, project manager, Perkins Technology Ltd. (Peterborough, England), in France, for example, 50% of the vehicles on the road are diesels. Is there a possibility of putting diesels in U.S.-built minivans, sport utility vehicles, and even passenger cars? Faulkner and his colleagues would like to think so. They recently completed a two-year program that resulted in a 3.0-liter, high-speed direct injection (HSDI), 170-hp, V6 diesel engine. He notes that this program was based on a simultaneous engineering team. Although the engine is, in effect, a feasibility study, inasmuch as Perkins isn't going to put an engine into production for which it has no customer, Faulkner notes, "This engine was designed for manufacture. It is production-compatible."
Ideally, Perkins is looking for a production volume of about 30,000 units to make this a practical product. And it has picked the sweet spots for the market: minivans, sport utes and passenger cars, but not just any passenger cars: they're looking at applications in luxury vehicles.
Diesels are well known for being noise vibration and harshness (NVH) oriented. So efforts to minimize NVH were at the top of the list of things to do by the simultaneous engineering team. And they paid off. According to Faulkner, the idle noise for the engine in a luxury car was measured at 49 dB, which is on par with a gasoline engine-equipped BMW or Jaguar at idle.
Because Perkins Technology is a consultancy, the outfit has an array of CAD/CAM/CAE resources that it put to use in the development of the 3.0-liter engine. Like the recently introduced New 1000 Series engines that Perkins launched for the construction equipment market (see "Mass Customization at Perkins," AMP, Feb. 97, pp. 42-45), this was a paperless development program. Among the tools employed is a analytical software program called Rumble. It was developed to simulate crankshaft motion within the powertrain. By simulating the loaded powertrain and the interaction of the crankshaft, bearing and cylinder block, the design of those elements can be optimized.
Would Perkins consider producing the 3.0-liter engine in the U.S. if an auto maker located here wanted the engine? The answer received from a Perkins spokesman came in the form of a smile, so while that is certainly not a "yes," it isn't a "no," either.
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