SkyActiv Naming
Essentially, SkyActiv is the nickname given by Mazda to a range of automotive technology solutions. This term encompasses not only engines but also includes chassis, transmissions, and more.
Here are some of Mazda’s definitions:
– SkyActiv G: This refers to Mazda’s new generation of engines, including 1.3, 1.5, 2.0, and 2.5 engines produced from 2012 until now.
– SkyActiv D: This term is used for turbo diesel engines.
– SkyActive Drive: This represents the next-generation automatic transmission.
– SkyActive Body: Mazda’s innovative body framework.
– Skyactive R: This refers to the Walken engine (rotary piston engine) that was developed from the previous generation on the RX7 and RX8 models with new technology.
– Skyactive – Hybrid: This represents the hybrid engine.
With its new design language, Mazda introduces incremental upgrades for each component cluster. However, in the Vietnamese market, mostly (or all) engines used are from the Skyactiv G generation, with the secret being a very high engine compression ratio compared to other engines. To learn more, let’s review the history of the development of naturally aspirated engines accompanied by compression ratios.
What is Compression Ratio?
For example, on a 2,000cc 4-cylinder engine, each cylinder has a volume of 500cc. At the largest volume, each cylinder contains a mixture of 500cc of air and fuel. This mixture is compressed, reducing its volume to 50cc when the piston reaches its limit. The formula for calculating the compression ratio is 500/50=10. Therefore, the compression ratio of this engine is 10.
What Limits the Increase in Compression Ratio?
When compressing the air-fuel mixture at high pressure and high temperature, there is a risk of premature combustion. This phenomenon is known as knocking, which can cause serious engine damage or, at the very least, produce annoying knocking sounds.
The knocking phenomenon is mainly determined by the fuel used. In the 1950s, the octane rating (knock rating) was around 70 octane, and most engines at that time had compression ratios of about 6.5. However, auto manufacturers were constantly looking for new methods to increase the engine compression ratio to generate more power from the same displacement, reduce fuel consumption, and emissions.
Here is the formula for calculating the power change when the compression ratio changes:
According to the above formula, increasing the compression ratio from 8 to 11 will result in an additional 9.2% power (Rnew = new compression ratio; Rorig = original compression ratio)
Although the main barrier is the fuel’s octane rating, auto manufacturers have applied various technologies to enable the use of higher compression ratios. In the 1950s, Mercedes produced the first Pullman vehicle that employed direct fuel injection (this technology is widely used today). The M198 engine used a compression ratio of 8.5, while most other engines used 6.5, which helped the Pullman achieve outstanding performance at that time.
Today, gasoline has improved significantly in terms of its octane rating. In Vietnam, RON95 gasoline is widely available, creating the basic condition for modern engines to run with compression ratios of 9.5 to 10.5. In 2001, BMW introduced the S54 engine with a relatively high compression ratio of 11.5 mounted on the BMW M3.
Mazda’s SkyActiv G Engine Generation
Returning to Mazda’s SkyActiv G engine generation. Introduced in 2012, Mazda’s engines have a high compression ratio of 14.0, and a series of technologies have been applied to overcome the barrier of knocking and provide better performance.
In particular, Mazda uses specially shaped pistons, fuel injectors in the form of streams, 4-2-1 exhaust systems, and improves the cooling system.
Improving the efficiency of many details in the SkyActiv engine results in a 15% fuel economy improvement and increased power. However, Mazda doesn’t stop there. They have announced their intention to release a new generation of SkyActiv engines with a compression ratio of up to 18.0 to achieve even higher performance. The launch is set to take place in 2019.
A graphic demonstrating the temperature reduction capability using a 4-2-1 exhaust system in the SkyActiv engine
An illustration showing the difference in pistons between SkyActiv engines and regular engines
Gaz69 (forum.autodaily.vn)
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