Hyundai Theta II 2.4-liter I-4 engine with Gasoline Direct Injection goes into production image

A new four-cylinder engine will help power Hyundai’s drive towards becoming the fuel economy leader when it launches in the company’s most popular car, the 2011 Sonata.

Today, Hyundai unveiled the engine, which is built at Hyundai Motor Manufacturing of Alabama, at its Hyundai America Technical Center in Superior Township, Michigan, where it engineers, designs, tests and certifies vehicles sold in the U.S.

The 2.4-liter Theta II GDI engine features gasoline direct injection (GDI) technology which operates with greater efficiency using less fuel, creating fewer emissions and delivering improved throttle response, all while making more power than a traditional port-injected engine. In the all-new 2011 Sonata, consumers can expect an estimated fuel economy of 35 miles per gallon in highway driving (EPA certification pending).

“At Hyundai’s core is a promise to deliver unparalleled quality and value to our customers,” says Hyundai Motor America President and CEO, John Krafcik. “Leading the introduction of this technology in our most important, highest volume product, the all-new 2011 Sonata, demonstrates our commitment to delivering products that excite and reward Hyundai owners.”

Theta II 2.4L GDI

Hyundai’s Theta I-4 engine family is a proprietary design, engineered in Namyang, Korea and currently in production for applications all over the world at volumes exceeding 2 million annually. The new Theta II 2.4L GDI engine is a derivative of the Theta with major upgrades in technology and architecture. It features a unique block, valvetrain, front end accessory drive (FEAD), intake manifold, pistons, rods, crankshaft, variable induction system and catalyst. The Theta II 2.4L GDI delivers an estimated 200 horsepower @ 6,300 rpm and 186 lb.-ft. of torque @4,250 rpm. The most significant technology in the new engine is direct injection.

How GDI Differs from Conventional Port Injection

The key to direct injection is the use of individual fuel injectors for each cylinder strategically positioned to deliver the optimal fuel charge directly into the combustion chamber. In a traditional multi-port system, gasoline is delivered via the port of each cylinder, where it mixes with air and is drawn into the cylinders when the intake valve opens and the piston moves down. A drawback to the traditional system is when engine speeds increase, the time to open the valve to deliver fuel becomes progressively shorter making accurate delivery more challenging.

GDI avoids that issue and the shorter, more direct path of fuel delivery, allows for greater control of the optimum fuel mixture at the optimum moment, thus improving efficiency. The fuel is injected by a camshaft-driven, high pressure pump that operates at pressures up to 2175 psi (150 bar). Direct injection also utilizes a higher than normal 11.3:1 compression ratio to for increased power. The pistons are “domed” to increase combustion efficiency.

The injection is split into two phases to achieve optimum combustion during the catalyst heating operation right after the cold start. First, the pilot injection is applied during the piston’s descent in the intake stroke and then, in the second, at the end of the compression stroke, the rest of the fuel is injected and then ignited after some delay. This split-injection technique reduces loading on the catalytic converter and helps lower emissions.

When an engine is cold, so is the catalyst. Traditional engines run high rpm’s for a few seconds upon startup to “fire” the catalysts. The GDI’s split-injection strategy enables the catalyst to reach operating temperature faster. This helps reduce emissions by 30 percent during cold starts meeting California Air Resources Board’s ULEV-2 and PZEV standards.