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Q&A: RKLAB AG on a new approach to clean up diesels

By Matthew Beecham | 22 October 2015

Gavin Houghton

Gavin Houghton

As the auto industry searches for affordable routes to lower emissions, Matthew Beecham spoke to Gavin Houghton, managing director of RKLAB AG to learn more about its timely breakthrough in diesel fuel injector technology.

Emissions legislation seems to be leading car manufacturers to increasingly desperate measures to produce compliant vehicles. How do you view the challenges they face?

Having made huge strides in reducing CO2 emissions in response to concerns over climate change, the industry is now faced with improving NOx and particulate emissions to combat deteriorating urban air quality. The big challenges are to achieve this without eroding the CO2 improvements or pushing vehicle costs higher than consumers will accept.

One of the industry's response has been to evolve the fuel injection process; each new generation using higher injection pressures (up to 3000 Bar) delivering through finer holes with more sophisticated rate shaping involving multiple injection events. This battle against the fundamentals of combustion chemistry has been supplemented by the use of exhaust gas recirculation (EGR) and increasingly sophisticated exhaust after-treatment, such as selective catalytic reduction (SCR) and diesel particulate filters (DPFs).

It has been estimated that up to 50 percent of the cost of a modern diesel or GDI engine is embedded in the fuel delivery system and its associated hardware. In addition to the cost issue, the increasing complexity of these modern systems makes long term reliability in service harder to achieve.

Technology development can also become counterproductive for example when DPF regeneration strategies increase fuel consumption, or higher pressure fuel pumps increase parasitic losses, harming engine efficiency. The current diesel technology has inherent trade-offs between fuel efficiency, NOx and particulate emissions. It is like a constant see-saw trying to balance these competing factors. This issue is clearly evidenced in the current VW crisis.

Is there an alternative approach?

The most effective approach would be to reduce the raw 'engine out' emissions from combustion so the after-treatment system has less work to do. In some cases this could even eliminate the requirement for after-treatment, while in others it could be greatly simplified and reduced in cost. The challenge is to achieve this without adding complexity to the engine or increasing mechanical losses. We believe the RK injector meets these goals.

How does the RK injector help?

It is self-pressurising, driven by cylinder pressure, which makes it fundamentally simple yet continuously self-adjusting, providing inherent, stepless rate shaping of the injector pulse. It also generates much higher pressures than any current system and can deliver the fuel through a large number of minute holes, up to 180, compared to six or eight in a current conventional injector. The shape of the fuel spray pattern is also quite different to conventional systems. Instead of forming a conical surface, the spray can take the form of a flat disc which makes both swirl and a traditional combustion bowl unnecessary.

How do these features improve combustion?

The higher pressures and finer holes create smaller fuel droplets, better mixing and cooler, more complete combustion, together reducing NOx and particulates and improving fuel economy. The natural feedback process within the RK injector, which takes its signal from the pressure in the combustion chamber, means the combustion curve of the fuel dictates the rate at which fuel is added; this optimises the rate of injection to eliminate over- or under-fuelling and adapts to different fuel characteristics.

The unique fuel spray pattern creates new possibilities for piston, combustion chamber and port design that could lead to lighter, more compact engines with better gas exchange. The finer atomisation produced by the RK injector also reduces the delay between injection and combustion, a fundamental constraint on the maximum useful rpm for a diesel.

How does it work?

Until the next raft of patent protection is in place, we have to keep much of the internal detail of the injector confidential. I can confirm that it uses an electro-hydraulic multiplier to magnify pressure, and high speed, high flow valving to control fuel delivery.

Apart from cleaning up emissions, does the technology have other implications for future engines?

The improved rate shaping of the injector pulse helps to reduce the peak rate of pressure rise during the combustion event. This leads to lower structural loads on the engine (up to 60 percent lower in tests) and improves NVH, reducing the characteristic diesel sound that is frequently, in the vernacular, described as 'diesel knock'.

Combined with the reduced combustion delay, this could bring diesel and gasoline engine architecture much closer together in future. The ability to extend the speed range while using a lighter cylinder block structure and a more compact piston design makes the potential for common hardware greater. We have trialled the technology on a number of gasoline engines converted to diesel operation, taking advantage of the lower peak cylinder pressure operation with promising results.

What stage of development has been reached?

The remainder of this interview is available on just-auto's QUBE Global light vehicle engine technologies market- forecasts to 2030