The first unit is a 2.4 litre four cylinder unit with a compression ratio of 11.3:1, and delivers 201ps at 6300rpm and 25.5kg.m of torque at 4250rpm in its initial Korean domestic market specification.
Developed at a cost of 170 billion won (£88 million) over a 46 month-long research period, the new 2.4 Theta II GDI engine will make its Korean debut in the first half of 2010. It is expected to appear in Kia products in the UK in 2011.
One serious limitation of conventional fuel injection systems is that as engine revolutions increase, the valve opening and closing times get progressively shorter, thus reducing the time available to inject fuel. GDI avoids this problem altogether by positioning the fuel injector in the most optimal location, directly inside the combustion chamber to offer unparalleled precision. With this shorter and more direct path, far greater control is attained over the combustion process: 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 percent during cold starts and meet's California Air Resources Board's ULEV-2 and PZEV standards
GDI's other benefits include improved dynamic performance and better fuel economy. Compared to a conventional engine of the same displacement, GDI delivers 7 percent more torque at low revolutions and 12 percent more torque at the high-end for better take-off and overtaking performance. And perhaps best of all, a vehicle equipped with a GDI engine will get about 10 percent better fuel economy than a vehicle equipped with a conventional multi-point fuel injected engine. Precise figures will vary according to the vehicle in which the engine is installed.
GDI has been applied to the second generation of Theta. Theta II 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. And the DCVVT system is governed by a new steel chain with an innovative 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.Kia Sorento updated for 2018
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