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Chevy Cruze diesel’s variable-swirl mechanism

073113-Chevrolet-Cruze-DieselEngine
The basic concept of GM’s variable swirl mechanism. Click to enlarge.

The 2014 Chevrolet Cruze Clean Turbo Diesel’s (earlier post) 2.0L engine uses a variable-swirl intake mechanism to enhance performance while reducing emissions. The variable-swirl intake manifold design optimizes air charge mixture motion in the cylinders for a more efficient combustion.

In Cruze’s variable-swirl intake manifold, each cylinder has two separate intake ports, with one of them controlled by a valve. During variable swirl, each throttle valve varies how much it opens to create mixture-motion of air and fuel within each cylinder. The effectiveness of any such variable mechanism is linked to the quality of its controls; GM’s engineering team spent a great deal of effort calibrating the actuator precisely to open and close the valves for optimal performance.

Use of variable swirl to enhance combustion has been studied in the industry literally for decades, with some work reaching back to the 1960s. GM was awarded a patent on one approach to an engine intake port with variable swirl vanes in 1984 (US Patent Nº 4,432,312). Optimizing swirl speed depending upon the engine operating condition is an effective means to increase thermal efficiency and reduce emissions, Toyota researchers noted in a paper in the R&D Review of Toyota CRDL in 2002.

In a study published in 2000, Dr. Paul Miles at Sandia National Laboratories found that:

Swirl ratio is found to exert a measurable influence on most of the combustion process, from ignition to late-cycle oxidation. Ignition delay decreases with increasing Rs, as do the magnitudes of the initial premixed burn, the peak rates of heat release, and the maximum rates of pressure rise.

A fixed geometry approach to providing fuel-air swirl is less than ideal because, in part, the amount of swirl delivered for part load is less than desired; on the other hand, the fixed geometry devices can restrict inlet flow under full load conditions. Thus, a range of approaches—including specially chamfered variable lift valves—have been developed to provide variable mechanisms to provide high swirl at lower loads and low restriction at full loads.

All combustion engines have swirl, but having variable swirl is a real difference maker for Cruze’s diesel engine. Ultimately, it means more driving satisfaction with less environmental impact.

—Mike Siegrist, 2.0L turbo diesel assistant chief engineer

Cruze’s diesel engine, mated to an automatic transmission, provides greater fuel economy than a comparably sized gasoline engine through greater thermal efficiency, a higher compression ratio and an unthrottled combustion process. Cruze’s diesel offers a segment-leading EPA-estimated 46 mpg highway (5.1 l/100 km) and range of more than 700 miles per tank.

Cruze Clean Turbo Diesel’s emissions will meet US Environmental Protection Agency’s (EPA) Tier 2 Bin 5 emissions standards.

Resources

  • Miles, P. (2000) The Influence of Swirl on HSDI Diesel Combustion at Moderate Speed and Load, (SAE Technical Paper 2000-01-1829) doi: 10.4271/2000-01-1829

Comments

dlmetzger63

The current VW 2.0L TDI engine has a swirl intake port and a fill intake port. The fill port has a valve in it that is opened and closed to regulate swirl. Conceptually these sound the same to me.

dlmetzger63

My above post forgot to state that this engine was released for 2009 model VW's for the US market. This is not new.

Peter_XX

This has been around for many years. If I recall correctly, the Opel 2-liter diesel engine developed in the mid-1990's had this feature. It has also been used on various gasoline engines over the years.

I was involved in experiments in this field some 25 years ago and learned a few basics from this. Variable swirl has some advantages at certain areas in the load and speed map. Obviously, the associated cost is not negligible; otherwise everybody would use it. For best result, you also have to design the inlet ports properly, so it is not a feature you could just add on any engine to obtain the benefits. A “substitute” is, as in many other cases, an improved injection system (e.g. higher pressure and/or different nozzle geometry).

litesong

In my homely 1979 Plymouth Champ(Dodge Colt), 2 valve per cylinder 1.4 liter 65 HP 4, a small 3rd valve operated at low rpms, to add extra swirl for better fuel economy. Sounded a bit theoretical, but worked well, as I featherfooted Champ to low rpm 42mpg average with a high of 50mpg. Champ operated for 22 years, till I sold it. I even saw it operating, 2 years after that.

Of course, I paid $4700 for Champ & the diesel Eco Cruze......$26000.....+. At 5.5 times the cost, auto manufacturers have found out how to make BIG money on econo cars.

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