Operating principles of the Common Rail Injection system.
Common rail injection systems are becoming increasingly common on today`s high-tech diesel engines. David Laidlaw, Komatsu Australia`s product manager, articulated dump trucks and large dozers, looks at the reasons why.
You may have started hearing the term `common rail injection` system in some recent television advertising for prestige diesel-engined cars.
Well, it`s also a term you`ll hear a lot more of in relation to earthmoving equipment.
Common rail injection (CRI) systems are delivering substantial benefits in terms of emissions and fuel consumption; they are seen by many as giving diesel engines the potential to become much cleaner than petrol engines in the future.
Komatsu, and a number of other heavy equipment manufacturers, are starting to introduce CRI system engines; in this article, I`ll look at how they work and what they mean for equipment owners and users.
First of all, what are the advantages of common rail injection systems?
In summary, they are as follows:
-- Cleaner / lower emissions and higher outputs due to high-pressure injection at in all usage ranges
-- More efficient combustion
-- Improved fuel efficiency
-- Reduction in noise and emission due to injection rate control
-- Improved performance due to increased flexibility in injection timing setting
-- Faster and smoother acceleration
-- Independent control of injection pressure in response to rotation and load.
How a CRI system works
Key CRI components are the supply pump, a `common rail`, an injector, sensors to detect running condition of engine and a computer (ECM) to control these devices.
A CRI system injects fuel to the engine at much higher pressures than conventional fuel injection systems. Typically, CRI injection pressures are around 20,000 psi, compared with 4000-5000 psi for a conventional system.
High-pressure fuel from the supply pump is distributed to an injector mounted on each cylinder by means of the common rail, with fuel injection quantity and timing determined by controlling the injectors.
Compared with conventional injection system characteristics, a CRI system has the following features:
-- Injected fuel quantity and injection pressure are independent of each other, and are definable for each and every engine operating condition, allowing optimum air/fuel mix formation
-- At the beginning of the injection process (during the ignition lag between the start of injection and the start of combustion), injected fuel quantities are very low.
Engine manufacturers have developed CRI systems as a method of getting diesel emission levels down to internationally specified standards.
You will have noticed that most new machines now being released have engines capable of meeting US and European `Tier II` emissions standards. In 2005, even more stringent `Tier III` standards will be introduced, and CRI engines will be essential to meet their requirements.
The end result is that equipment fitted with such engines produces substantially lower emissions than earlier models -- even those just a few years old.
The other major advantage is in fuel consumption -- which goes directly to a machine owner`s bottom line.
Typically, CRI engines provide fuel savings of 10-20% compared with equivalent sized earlier-model machines.
It has to be said that in Australia, CRI engines are not yet able to meet their full potential in terms of emissions levels and fuel consumption due to relatively high sulphur levels still allowed in Australian diesel.
Our sulphur PPM levels are significantly higher than those permitted in the US or Europe, but the federal government is about to introduce pricing incentives to encourage rapid take up of low sulphur fuel. High-sulphur fuels will be phased out in the next few years.
However, even with our high sulphur PPM levels, the high-pressure, clean-burning CRI engines are substantially more fuel efficient and less polluting. It`s just that the best is yet to come.
By : David Laidlaw,
Komatsu Australia`s Product Manager, articulated dump trucks and large dozers
Sumber : www.komatsu.com.au