Mazda will have out-engineered GM, Daimler, and Hyundai, all of which have tried and failed to develop HCCI engines in a cost-effective package.其他幾家都搞過是成本問題。
SkyActiv engines will employ HCCI technology, improving fuel economy by 30 percent and at the same time reducing exhaust emissions.
HCCI burns the air/fuel mix using pressure instead of with spark plugs, just like a diesel. At 14:1, Mazda's gasoline engines already have some of the highest compression ratios out there, but a move to HCCI means cranking up the compression to 18:1.這個18:1對發動機block要求還是挺高的
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Advantages
- Since HCCI engines are fuel-lean, they can operate at diesel-like compression ratios (>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.
