Feature December 1, 2011 by
Tom Venetis, Editor SSGM Magazine
GDI Engines Becoming Mainstream Technology
Gasoline Direct Injection technology is nothing new.It was first introduced by Jonas Hesselman in 1925. His engine design operated by the ultra lean burn principle and worked by injecting fuel in the end of the compression stroke which was...
Gasoline Direct Injection technology is nothing new. It was first introduced by Jonas Hesselman in 1925. His engine design operated by the ultra lean burn principle and worked by injecting fuel in the end of the compression stroke which was ignited by a spark plug. The technology was later used in aircraft engines during the Second World War. Gasoline engines using the technology were developed by Bosch in 1952, with the Gutbrod Superior 600 and the Goliath 700 GP being the first vehicles to use the technology. It was later followed by Mercedes 300 SL in 1954. Today, the technology has been incorporated in a wide variety of engines from Ford’s EcoBoost-based family of vehicles to the new Hyundai Sonata. Gasoline Direct Injection technology offers several advantages over traditional fuel injection systems. With more precise physical designs and the use of computer management, Gasoline Direct Injection engines give much more control over fuel metering and injection timing. Because of the location of the injector, there is a more precise and optimal spray pattern, one that breaks up the gasoline into smaller droplets. This results in an engine that operates more efficiently and produces less harmful emissions. “Gas Direct Injection (GDI) is becoming more popular due to increasing demands for lower emissions and higher fuel economy,” said Dave Hobbs, DPSS Service Trainer with Delphi Automotive. “Many passenger cars and light-duty trucks with gasoline engines have been migrating towards this advanced fuel injection technology over the past several model years. The largest driving factor is the increased CAFE (Corporate Average Fuel Economy) slated for the 2016 model year where the federal government has proposed to increase it from 27.5 MPG to 35.5 MPG.” But the new technology poses several challenges which independents should be aware of. Marcus Lyons, ACDelco TSS Manager said the first thing to be aware of is these new engines “use (a) much higher fuel deliver pressure and there are inherent concerns that this should be observed when dealing with any media under high pressure.” “GDI equipped vehicles have their fuel injectors mounted directly inside the cylinder and the injection spray occurs during the piston’s compression stroke,” added Hobbs. “This arrangement is much like those used on modern diesel engines. GDI requires a much higher spray within the injector to overcome the amount of pressure created in the cylinder by the upward moving piston.” Many GDI systems also use a lower pressure pump to move the fuel from the tank to the engine, along with an additional mechanical pump to boost the pressure into the direct injection fuel rail. Pressures can reach up to 200 atmospheres or 3,000 PSI, according to Hobbs. If one has worked on modern diesel technologies, then this is not something new. And one is certainly familiar with the safety precautions needed when working with those kinds of engines and pressures. “When the pressure goes into the levels of GDI and diesel injection, the pressure can be great enough for a leak to cause a fine stream of fuel with enough power to break the skin of even the toughest hand,” added Hobbs. “Any liquid with enough pressure behind it can literally cut like a surgeon’s scalpel. The actual breaking of skin isn’t much of a concern, as blood poisoning that could potentially occur after such an accident.” Another issue that has often come up with GDI system is efficiency loss due to deposits on the piston surfaces and intake ports and valves. This is the result of the constant challenge of balancing economy and environmental concerns when it comes to fuel formulations. Prior to detergents, some gasoline blenders made changes to fuels that caused some engines to develop carbon deposits on the back of intake valves which reduced air flow into the cylinder and absorbed some of the fuel spray on cold starts. To the driver, this appeared as cold start hesitation and stalling. When detergents were added to the fuel, carbon deposits became less of an issue. “Moving forward to today’s GDI engines, we see a similar problem coming back in a few vehicles,” Hobbs said. “With GDI’s move of the injector directly into the cylinder, no matter how good the fuel detergents are, there is no fuel being sprayed at the backs of the intake valves. Plus, oil fumes (blow-by gasses) from the crankcase/PCV system are still, as they have been for years, creating some of their own deposits in intake manifolds on the back of intake valves. “In response, Volkswagen has begun using the old walnut shell blaster procedure to clean up their GDI equipped vehicles. Other OEMs are joining in with the old cure for this carbon problem that keeps reinventing itself.” ACDelco’s Lyons added with any new technology, these issues are being addressed by the OEMs. However, he strongly recommended technicians begin to get training on GDI engine technologies as they will require some new skills and knowledge to successfully service. As an example, GDI engines have unique mechanical and electrical differences. Removing the injectors, for example, will require special pullers and the inspection and replacement of the injector O-rings. Some of the low-pressure fuel pumps used in some vehicle models are made to run at different speeds due to a variable voltage control module which is controlled by a CAN bus message by the ECM. The ECM, in turn, monitors the fuel rail pressure with a new sensor “which means the service technician now has a new scan tool PID to watch and understand,” added Hobbs. “Like anything else new, make sure you are educated on the latest systems before they come into your shop.”