Continued from Mazda Revamps Diesel Engine for 'CX-8' SUV (2)

In addition, the remodeled engine promotes the premixing of fuel and air by forming fine particles of fuel with a high pressure at the time of normal driving. Furthermore, Mazda said that it has developed a technology to mix fuel and air well by making improvements to the method of making fuel and the injector though the company did not disclose the details of the technology.

With those improvements, it became possible to shorten the time it takes for fuel to be mixed with air without compromise of environmental performance and, therefore, to increase compression ratio.

The waveform of the heat release rate of high-speed multi-stage combustion. In the past, combustion formed multiple mountains. This time, combustion forms one mountain because of short-interval, multi-stage injection.

The maximum injection pressure of the injector is the same as that of the CX-5's injector. Also, the number of injection ports (10) did not change.

On the other hand, the response of the needle valve that opens and closes the injection nozzle was improved, and it became possible to set the injection pressure at the time of normal driving at a level 20-30% higher than before. The improved response enables to open and close the injection nozzle at high speeds, preventing fuel from spilling at the time of closing the nozzle.

As a result, it became possible to shorten the interval between fuel injections as much as possible, enabling to inject fuel more frequently and at more appropriate timings and realize more ideal combustion.

Mazda made other efforts to improve fuel efficiency such as (1) employing a stepped egg-shaped piston to reduce cooling loss and (2) hardly flowing cooling water when the temperature is low by using a cooling water control valve in the aim of accelerating the warming of the engine and reducing the resistance of lubricant.

The stepped egg-shaped piston. There are steps on the upper surface of the piston.

The cooling water control valve

The engine also features low-noise operation. Mazda prevented rapid pressure increases caused by combustion to reduce knocking sound. Specifically, the company finely controlled the amount of fuel injected and prevented the inclination of heat generation at an early stage of combustion to solve the problem of rapid pressure increases.

Original Japanese article