Mazda makes gasoline engines as efficient as diesel

Mazda Motor Corp said it would become the world’s first automaker to commercialize a much more efficient petrol engine using technology that deep-pocketed rivals have been trying to engineer for decades, a twist in an industry increasingly going electric.

The new compression ignition engine is 20 percent to 30 percent more fuel efficient than the Japanese automaker’s current engines and uses a technology that has eluded the likes of Daimler AG and General Motors Co.

Mazda, with a research and development (R and D) budget a fraction of those of major peers, said it plans to sell cars with the new engine from 2019.

The engine is called SKYACTIV-X and Mazda had no plans to supply the engine to other carmakers.

HCCI engines achieve extremely low levels of Oxides of Nitrogen emissions (NOx) without a catalytic converter. Hydrocarbons (unburnt fuels and oils) and carbon monoxide emissions still require treatment to meet automotive emission regulations.

Advantages

Since HCCI engines are fuel-lean, they can operate at diesel-like compression ratios (over 15), thus achieving 30% higher efficiencies than conventional SI gasoline engines.
Homogeneous mixing of fuel and air leads to cleaner combustion and lower emissions. Because peak temperatures are significantly lower than in typical SI engines, NOx levels are almost negligible. Additionally, the technique does not produce soot.
HCCI engines can operate on gasoline, diesel fuel, and most alternative fuels.
HCCI avoids throttle losses, which further improves efficiency.

Disadvantages
Achieving cold start capability.
High heat release and pressure rise rates contribute to engine wear.
Autoignition is difficult to control, unlike the ignition event in SI and diesel engines, which are controlled by spark plugs and in-cylinder fuel injectors, respectively.
HCCI engines have a small power range, constrained at low loads by lean flammability limits and high loads by in-cylinder pressure restrictions.
Carbon monoxide (CO) and hydrocarbon (HC) pre-catalyst emissions are higher than a typical spark ignition engine, caused by incomplete oxidation (due to the rapid combustion event and low in-cylinder temperatures) and trapped crevice gases, respectively

Homogeneous charge compression ignition (HCCI) is a form of internal combustion in which well-mixed fuel and oxidizer (typically air) are compressed to the point of auto-ignition. As in other forms of combustion, this exothermic reaction releases energy that can be transformed in an engine into work and heat. HCCI combines characteristics of conventional gasoline engine and diesel engines. Gasoline engines combine homogeneous charge (HC) with spark ignition (SI), abbreviated as HCSI. Diesel engines combine stratified charge (SC) with compression ignition (CI), abbreviated as SCCI.

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