Developed with a budget of 170 billion won (US$147 million) over a 46 month-long research period, the new 2.4 Theta II GDI engine will make its debut in the first half of 2010 starting with the recently launched Sonata. GDI application will subsequently be expanded across the gasoline engine family and applied to other Hyundai models.

Hyundai had shown a 2.0-liter concept Theta turbocharged gasoline direct injection (GDI) four-cylinder engine capable of developing as much as 286 hp (213 kW) while and delivering more than 30 highway mpg at the Los Angeles Auto show in 2008. (Earlier post.)

in the new production 2.4 Theta II GDI, a high pressure fuel pump injects the fuel at pressures of up to 150 bar, in precise amounts and intervals. The injection is split into two phases to achieve optimum combustion: in the first phase, the pilot injection and ignition trigger the piston’s downward power stroke. Then, in the main injection phase, during the piston’s descent, more fuel is injected and is ignited.

This split-injection technique reduces loading on the catalytic converter and helps lower emissions. This is particularly beneficial during cold starts when emissions are highest because the catalyst has not reached its optimal operating temperature. Split-injection enables the catalytic converter to reach the optimal operating temperature faster thus reducing emissions by 25% during cold starts and meet’s California Air Resources Board’s ULEV-2 and PZEV standards.

Theta II, the second-generation of Theta, features numerous design enhancements over its predecessor starting with the application of a three-stage variable induction system (VIS) which improves engine breathing, automatically adjusting the volume of the air sucked into the combustion chamber to create the optimal air-to-fuel mix under different engine load conditions.

Further performance gains were made possible by incorporating Dual Continuously Variable Valve Timing (DCVVT) which improves engine breathing on the intake and exhaust sides for better fuel economy and lower emissions. Depending on engine load and speed, DCVVT can extend or shorten the duration of the valve opening and closing for more power and lower emissions. The DCVVT system is governed by a new steel chain with a novel roller and tooth designed for silent operation and durability.

While DCVVT and VIS improve power output, engineers have also come up with several important weight saving innovations. Special attention was focused on the bulkhead, the area of the aluminium cylinder block accumulating the highest stresses—reinforcement yielded a stiffer block without incurring a weight penalty. A redesign of the crankshaft (semi-eight-balance type) led to an equally important weight reduction. The catalytic converter is also lighter thanks to a new canning process which allows for the use of thinner gauge stainless steel and requiring far less welding.

Another major engineering challenge was to reduce internal friction to attain better fuel economy. Friction reduction measures include a revision of the piston pin from a fixed-type to a full-floating design which cuts down on friction between the piston and cylinder wall. And under the piston crown, engineers have added a cooling jet which sprays oil over the piston walls reducing friction and contributing to an improvement in fuel economy.

Some 600 specialists from Europe, Japan, the United States and Korea are attending the powertrain event.