Additionally, it was forecast that by the end of 2008, GM will produce as many as 200,000 vehicles globally with direct injection technology, and by 2010, GM projects one out of every six GM vehicles in North America will be equipped with a direct injection engine.
The application of direct injection technology to the 3.6-liter VVT engine – a member of GM Powertrain’s family of high-feature V-6 powerplants used on cars and trucks around the world – contributes greatly to a 15-percent increase in horsepower over the current levels that range from 240 to 267; an 8-percent increase in torque, and up to a 3-percent improvement in brake-specific fuel consumption (BSFC). An approximate 25-percent reduction in cold-start hydrocarbon emissions is also achieved.
With direct injection, precisely metered fuel is delivered directly to the combustion chamber, which has a cooling effect in the chamber. Cooling the incoming air charge enables a higher compression ratio, which also improves engine efficiency. Less fuel is required to produce the equivalent horsepower of a conventional port injection combustion system.
“The 3.6-liter VVT with direct injection will be our highest specific output non-turbocharged V-6 engine, as well as one of the most fuel-efficient offerings in our high-feature family,” said Tim Cyrus, chief engineer for high feature V-6 and Northstar V-8 engines. “It’s the latest example of our strategy to continue to reduce emissions and improve fuel economy without sacrificing performance.”
This is GM’s third engine with gasoline direct injection. The announcement of the 3.6L VVT V-6 with direct injection comes on the heels of the introduction of GM Powertrain’s Ecotec 2.0-liter four-cylinder Turbo engine with direct injection on the 2007 Saturn Sky Red Line and Pontiac Solstice GXP roadsters. Also, since 2004, a naturally aspirated Ecotec 2.2-liter direct injection engine is equipped on Opel models in Europe.
How direct injection works
Direct injection differs from the fuel delivery process of a conventional engine by delivering fuel directly into the engine cylinder, where it is mixed with air. The combustion process of conventional fuel injected engines uses air and fuel that partially evaporates in the intake port or intake manifold prior to being introduced into the combustion chamber. Direct injection is a continuation of the evolutionary process of moving the fuel introduction point closer to the cylinder to improve control.
With the 3.6-liter VVT with direct injection, fuel is introduced directly to the cylinder during the intake stroke. As the piston approaches top-dead center, the mixture is ignited by the spark plug.
The fuel injectors are located beneath the intake ports. The intake ports only transfer air, unlike port fuel injection, which flows air and fuel, thus increasing efficiency. D irect injection also permits a slightly higher compression ratio than if the fuel were delivered with conventional fuel injection. The result is better fuel consumption at part and full throttle. The engine uses conventional spark plugs similar to other high-feature V6 engines.
A high-pressure, returnless fuel system is employed. It features a high-strength stainless steel fuel line that feeds a variable-pressure fuel rail. Direct injection requires higher fuel pressure than conventional fuel injected engines and an engine-driven high-pressure fuel pump is used to supply up to 1,740 psi (120 bar) of pressure. The system regulates lower fuel pressure at idle – approximately 508 psi (35 bar) and higher pressure at wide-open throttle. The exhaust cam-driven high-pressure pump works in conjunction with a conventional fuel tank-mounted supply pump.
Direct injection’s fuel delivery enables very efficient combustion to help reduce emissions, particularly on cold starts – the time when most tailpipe emissions are typically created. Also, direct injection permits a higher compression ratio – greater than 11.0:1 in the case of the 3.6 – which has a positive influence on fuel economy.
3.6-liter VVT DI
The 3.6-liter VVT DI is based on GM Powertrain’s sophisticated 60-degree dual overhead cam (DOHC) V-6 engine. It is the latest member of a growing family of GM Powertrain V-6 engines developed for applications around the world, drawing on the best practices and creative expertise of GM technical centers in Australia, Germany, North America and Sweden.
Features found on the 3.6-liter VVT DI include:
- Aluminum engine block and cylinder heads
- Dual overhead cams with four valves per cylinder and silent chain primary drive
- High-pressure, engine-driven fuel pump
- Advanced multi-outlet fuel injectors developed to withstand high pressure and heat
- Stainless steel, variable pressure fuel rail
- Four-cam phasing (VVT – see description below)
- 11.3:1 compression ratio
- Aluminum pistons with floating wrist pins and oil squirters
- Polymer coated piston skirts
- Forged steel crankshaft
- Sinter-forged connecting rods
- Structural cast-aluminum oil pan with steel baffles
- Electronic throttle control with integrated cruise control
- Coil-on-plug ignition
- Advanced direct injection capable engine control module (ECM)
- Optimized exhaust manifolds with close-coupled catalytic converters
- Fully isolated composite camshaft covers
- Outstanding noise, vibration and harshness control
- Maximum durability with minimum maintenance
- Common manufacturing practices for efficiency and exceptional quality
The 3.6-liter V-6 VVT DI employs four-cam phasing to change the timing of valve operation as operating conditions such as rpm and engine load vary. The result is linear delivery of torque, with near-peak levels over a broad rpm range, and high specific output (maximum horsepower per liter of displacement) without sacrificing overall engine response and driveability. When combined, direct injection and cam phasing technologies enable an unmatched combination of power, efficiency and low-emissions in gasoline V-6 engines.
Cam phasing pays big dividends in reducing exhaust emissions by optimizing exhaust valve overlap and eliminating the need for a separate exhaust gas recirculation (EGR) system.
By closing the exhaust valves late at appropriate times, the cam phasers allow the engine to draw the desired amount of exhaust gas back into the combustion chamber, reducing unburned hydrocarbon emissions. The return of exhaust gases also decreases peak temperatures, which contributes to the reduction of oxides of nitrogen (NO x) emissions. In tandem with the dramatic 25-percent reduction in cold-start hydrocarbon emissions brought on by direct injection, the 3.6-liter VVT DI V-6 surpasses all emissions mandates, and does so without complex, weight-increasing emissions control systems such as EGR and air injection reaction (AIR).