More efficient and even more powerful. [fimg=right]http://www.cleanmpg.com/photos/data/501/SKYACTIV-G_Piston.jpg[/fimg]Wayne Gerdes - CleanMPG - Nov. 6, 2011 The all-new Mazda 2.0L gas engine’s piston. The cavity is reminiscent of the diesel with a much more controlled flame front without interference vs. the somewhat flat face of a standard gasoline engine piston. The all in end result? 40 mpgUS highway, 155 HP@6,000 rpm and 148 lb-ft of torque@4,100 rpm without turbocharging. Mazda’s all-new range of SKYACTIV technologies are designed to improve the efficiency of the company’s next generation of vehicles while at the same time further enhancing safety and driving dynamics. Innovation is at the key with a focus on optimizing the internal combustion and lightweight engineering. These technologies will be implemented into all future models — not just expensive “green” variants — in order to benefit all Mazda customers. SKYACTIV-G 2.0L Gasoline Engine – Mazda’s quest for ideal combustion A range of new technologies has gone into the highly-efficient direct injection SKYACTIV-G gasoline engine. These include taking compression to an all-new level in order to increase thermodynamic efficiency and solving the issues that until now have prevented this approach from being feasible. SKYACTIV-G 2.0L Highlights Exceptionally high 13:1 compression ratio in North America (14:1 in other markets due to a higher fuel octane) Extraordinary compression ratio made possible thanks to a 4-2-1 exhaust system, redesigned piston cavity, new multi-port injectors as well as other innovations to avoid abnormal combustion (“knocking”). Continuously variable sequential valve timing (dual S-VT) on the intake and exhaust minimizes pumping losses. Internal engine friction reduced by 30 percent. Overall weight reduced by 10 percent. Approximately 15 percent lower fuel consumption and CO2 emissions than the current Mazda 2.0-liter MZR gasoline engine. Approximately 15 percent more torque at lower and mid-range rpms. The principal goal of Mazda’s engineers when developing its SKYACTIV technologies was to dramatically increase vehicle efficiency for all next-generation vehicles by improving fuel economy while further enhancing safety and driving fun. And, they have managed to successfully reconcile these conflicting objectives with the completely new SKYACTIV range of engines, transmissions, body architecture and chassis that will go into Mazda’s next generation of models beginning in 2012. Internal combustion engines will still power between 80 and 90 percent of vehicles in 2020. Unfortunately, today’s gasoline fueled engines operate at only 30 percent efficiency and thus the need of improvement. Mazda’s engineers focused on one objective: achieving ideal combustion. Therein lays the basis for Mazda’s SKYACTIV-G gasoline engines in all next-generation models and not just pricey “green” models. One of Mazda’s core business objectives is to make personal mobility environmentally friendly and affordable for a broad section of the population. This is why Mazda has made it a priority to increase the efficiency of its internal combustion engines. The company’s R&D staff in Hiroshima sought the best means of achieving a significant optimization of processes within this basic engine architecture, steadily and broadly reducing fossil fuel consumption. Engineering the ideal internal combustion engine Even after 120 years of non-stop development the internal combustion engine still fails to utilize 70 to 90 percent of the energy contained in the fuel. Since this energy loss is primarily thermal in nature and can be attributed to the exhaust, cooling system, and engine and transmission surfaces, the R&D team’s central focus was on improving the engine’s thermal efficiency. Beyond that, Mazda has also been busy working to reduce internal engine friction as well as engine weight. The six controllable factors at the heart of this approach are: Compression ratio Air-to-fuel ratio Combustion duration Combustion timing Pumping loss Mechanical friction loss The goal was to optimize these factors in unison and making them function as optimally as possible. Ultimately, the compression ratio would end up playing a central role among the factors listed. [fimg=left]http://www.cleanmpg.com/photos/data/501/SKYACTIV_Comp_Ratio.jpg[/fimg]SKYACTIV-G Compression Ratio and TDC Temperatures. The advantages of the unique direct-injection SKYACTIV-G gasoline engine are the result of Mazda’s unique “breakthrough” engineering approach. By thoroughly analyzing and rethinking common thermodynamic principles, engineers succeeded in building an engine with an extraordinarily high 13:1 compression ratio. This is a level only seen thus far in high-performance race car engines not intended for everyday use. Mazda has overcome these barriers. Any discussion about the compression ratio needs to examine the advantages and challenges of high compression. Raising the compression ratio in a gasoline engine increases its thermal efficiency, thus improving fuel economy. However, high compression in conventional engines leads to unwanted abnormal combustion (known as “knocking”) and an associated reduction in torque. A richer mixture and delayed ignition timing are used to avoid knocking, but these also come at the expense of fuel economy and torque. So how were these issues overcome? High compression without knocking The combustion duration was also reduced. Faster combustion shortens the time the unburned air-fuel mixture is exposed to high temperatures, which enables normal combustion to conclude before knocking occurs. The new engine also received special piston cavities, which allow the initial combustion flames to propagate without interference, and new multi-hole injectors, which enhance fuel spray characteristics. Together with the 4-2-1 exhaust manifold, these innovations resulted in a substantial 15 percent increase in torque over Mazda’s current 2.0L MZR gasoline engine. Everyday drivers will love the SKYACTIV-G’s noticeably higher torque over a wide range of rpms as well as its 15 percent improved fuel economy. Valve Overlap and the Resultant Output Characteristics Minimizing pumping losses To improve engine efficiency, it is also necessary to reduce the “pumping loss” that occurs at lower engine loads when the piston draws in air while moving downward during the intake stroke. Generally, the amount of air going inside the cylinder is controlled by the throttle located upstream of the intake pipe. At lower engine loads, only a small amount of air is necessary. The throttle is nearly closed, causing the pressure inside the intake pipe and cylinder to be lower than the atmospheric pressure. As a result, the piston has to overcome a strong vacuum. This is known as pumping loss, which negatively affects efficiency. Mazda managed to minimize pumping loss with a continuously variable dual S-VT (sequential valve timing) on the intake and exhaust valves. This changes the opening and closing timing of the valves, enabling the air intake quantity to be controlled by the valves rather than the throttle. During the intake stroke, the throttle and intake valves are kept wide open while the cylinder moves downward. The intake stroke finishes when the piston reaches the cylinder bottom (bottom dead center or BDC). But if the intake valves close here, there is too much air inside the cylinder when only a small amount of air is needed at lower engine loads. In order to push out the excess air, the intake S-VT keeps the intake valves open when the piston starts to move upward during the compression stroke. The intake valves then close when all unnecessary air is pushed out. This is how an S-VT minimizes pumping loss, making the overall combustion process more efficient. A drawback to this process is destabilized combustion. Since the intake valves are kept open even when the compression stroke starts, the pressure inside the cylinder decreases, making it difficult for the air-fuel mixture to combust. This is not a problem for the SKYACTIV-G, however, thanks to its 13:1 compression ratio. The high compression ratio increases combustion chamber temperature and pressure, so the combustion process remains stable — despite reduced pumping loss — and the engine is more fuel efficient. Reducing weight and internal engine friction A vehicle’s overall responsiveness can be enhanced by decreasing the size and weight of its components. And a complete engine redevelopment project presents the opportunity to forge new paths when it comes to lightweight design. With 20 percent lighter pistons, 15 percent lighter connecting rods and a 30 percent reduction to internal engine friction compared to the current 2.0-liter MZR engine, the new SKYACTIV-G power plant is gleefully free-revving, adapts faster to load changes and thus bolsters the sporty character of the Mazda it powers. With less energy expended in the process, fuel economy is improved by 15 percent compared to the current engine. This was a presentation to Automotive Journalists given in Vancouver BC earlier this year. We will have more on the Diesel, the 6-speed MT and AT and even the new lightweight body structures Mazda has put together for their all encompassing and fuel efficient SKYATIV programs just now reaching the consumer through the Mazda3 and many future Mazda vehicles to come.