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Study explores impact of alcohol-gasoline blends with early inlet valve closing at low and moderate loads on EGR tolerance

A team from Brunel University, MAHLE Powertrain and University College London studied the combined effects of different inlet valve operating strategies on combustion, performance and emissions with different ethanol and 1-butanol blends with gasoline in a single-cylinder spark-ignition research engine equipped with a fully variable valvetrain. Their paper is published in the journal Fuel.

The focus was to better quantify the effects of alcohol content and Early Inlet Valve Closing (EIVC) operation on EGR tolerance under the lowest speed-load conditions typically encountered (e.g., engine idle) while also quantifying the changes in optimum valvetrain settings at moderate speeds and loads where the effects of varying EGR tolerance were less dominant.

Variable valve timing is an established technique for improving the fuel economy of a gasoline engine via several mechanisms. There is growing interest in fully variable valvetrain systems for further reduction in throttling losses via load control directly and the inlet valves, and increased thermal efficiency through a greater effective expansion ratio.

While numerous fully variable valvetrain strategies are possible depending upon the application, other studies have highlighted the use of Early Intake Valve Closing (EIVC) as a favorable strategy at part load, the authors noted.

The researchers also noted the significant global interest in alcohol fuels for SI engines.

Compared to gasoline, the lower alcohols exhibit high latent heat of vaporisation and anti-knock rating, which makes them attractive for use in future “downsized” highly boosted SI engines that endure significantly higher peak in-cylinder pressures and temperatures. Such downsizing may help offset the low energy density of ethanol, while problems with cold star due to reduced volatility can also be reduced via, for example, advanced DI operating strategies. However, gasoline-ethanol blends are known to exhibit azeotropic behaviour, with profound effects on the vaporisation and thermodynamic properties of the blend.

...Elsewhere, “higher” alcohols such as propanol, butanol and pentanol have also been considered for automotive use. From a thermodynamic stance the higher alcohols generally exhibit favorable calorific value (and hence better volumetric fuel consumption), better water tolerance, volatility control and lower Reid vapour pressure. However, the increased molecular carbon chain reduces the available hydrogen bonding effect and benefits in latent heat (charge cooling) and hence knock resistance are typically reduced.

—Cairns et al.

The study explores the interaction of these two technology threads—i.e., VVT and alcohol biofuels.

The worst case engine operating condition for SI engine EGR tolerance is normally engine idle, where the low speed and low load lead to minimum in-cylinder gas pressures and temperatures, reduce in-cylinder charge motion levels, decreased burning velocities and relatively high cylinder wall heat transfer losses.

In the testing, the team set the engine to EIVC operation at idle and then attempted to increase the valve overlap until the acceptable combustion stability limit was approached.

The researchers used a naturally aspirated single cylinder four-valve per cylinder spark ignition research engine. The cylinder head included a prototype mechanical variable valvetrain assembly, fitted to both the inlet and exhaust. The system is an evolution of MAHLE’s Variable Lift and Duration (VLD) mechanism. The system is based on a shaft-in-shaft cam operating principle. The opening and closing control cams act in tandem to produce a mean cam (and valve) lift curve. By advancing the phasing of the inner shaft relative to the outer shaft, the closing of the valve is advanced, allowing reduced lift and duration.

The phasing of the closing control cam was controlled with a prototype wide range hydraulic cam phaser (VLD Phase). To achieve fully variable valvetrain operation, a second hydraulic VVT Phaser was fixed to the other end of the entire camshaft assembly.

Fuels tested included a commercial UK pump-grade unleaded gasoline (95 RON) as a baseline; iso-octane (i100), ethanol (E100); 1-butanol (Bu100), and 25% splash blends of ethanol and 1-butanol with gasoline and the iso-octane.

The experiments involved study of EIVC at varied degrees of valve overlap. The inlet valvetrain was variable in duration/lift and timing, whereas the exhaust valve actuation was only variable in timing.

Among the findings were that:

  • During warm idle operation, high ethanol content fuels allowed significant improvement in tolerance to internally recycled burned gases. At lowest load conditions, this allows higher valve lifts to be used, with reduced throttling locally at the inlet valves, further small fuel savings and reductions in engine-out emissions of NOx.

    For example, when using E100, the overlap was increased from 15° to 33° crank, resulting in a small additional fuel consumption savings of ~2.7% compared to EIVC-only operation.

    The authors attributed this to the faster laminar burning velocities of ethanol and faster rates of mass burning.

  • 1-butanol content, regardless of the percentage of the blend, appears not to influence EGR tolerance.

  • Use of high ethanol content fuels at idle enabled moderate reductions (up to 20%) in engine-out NOx, primarily associated with significant increase in the residual mass tolerated.

  • For all ethanol fuels, increasing the valve overlap reduced the combustion efficiency (qualitative reduction of ~1.7% for E100, for example.

  • At moderate speeds and loads, where throttling losses were less, the valvetrain could still be used to attain additional thermal efficiency improvements including reduced compression losses and further expansion work for all fuels.

    However, a trade-off with increased pumping losses during the exhaust stroke was apparent, with the throttling moved from the inlet to the exhaust valves at the most retarded valve timings studied.

  • For all fuel blends, variable valve timing alone offered the greatest NOx reduction potential at moderate loads, insinuating the ability to operate variable valve timing with and without early intake valve closing may offer one viable path to meeting future engine emissions targets.

Resources

  • Alasdair Cairns, Hua Zhao, Alan Todd, Pavlos Aleiferis (2013) A study of mechanical variable valve operation with gasoline–alcohol fuels in a spark ignition engine, Fuel, Volume 106, Pages 802-813 doi: 10.1016/j.fuel.2012.10.041

Comments

Jus7tme

EGR = Exhaust Gas Recirculation, someone had to say it.

HarveyD

It is interesting to note how a dying technology (ICEs/ICEVs) is being improved in the last 5 years or so.

However, it is too late for (ICEs/ICEVs) to survive with the possible exception for large trucks, ships, heavy machinery and airplanes with the above research etc and the help of Oil industries...

Jus7tme

Why does HarveyD continue to dismiss engine technology improvement, including hybrid cars, which are he best CO2/mile technologies, better than electric cars and plug-ins?

Well, I think HarveyD has an agenda: He wants increased demand and higher prices for Quebec hydroelectric power, via demand created from electric cars.

But is what he wants the right thing to do? No, it is not, because what Canada SHOULD do is turn off their coal plants and use the hydropower themselves for already existing demand. Why does Canada not do that, you ask?

My guess would be that the political establishment is protecting the profits of the coal-based power industry. And the fraction of fossile electricity in the Canada electrical grid mix is INCREASING:

2007 numbers for Canada say 59% hydro and 19% fossile, Reference: http://www.ec.gc.ca/default.asp?lang=En&n=714D9AAE-1&news=0A6CF209-AF7A-4913-A27F-527B4ECF811B

2012 numbers for Canada say 59% hydro and 23% fossile, Reference: http://www.esu-services.ch/fileadmin/download/publicLCI/itten-2012-electricity-mix.pdf

To summarize, HarveyD's motivations are not pure. Personally I care about two things: ONE: Using as little oil andd gas as possible, leaving it in the ground for future generation. TWO: creating as little CO2 as possible.

The solution is for everyone to switch to the most efficient hybrid cars, getting 50 mpg today and easily getting 70+ mpg when diesel hybrids become available to the mass market.

Already, a Toyota Prius emits less CO2/mile than the much smaller small NIssan Leaf Electric car, when running on the heavily fossile-based US electrical grid mix.

HarveyD

J7t...my wife drives a new Prius III HEV and I'll probably buy a 2014 Camry Hybrid HEV late this fall.

The only reason we do not use PHEVs today is the current lack of appropriate charging facilities. This is difficult to accept in an area with a huge surplus of clean, very cheap Hydro electricity?

The main reason we do not use BEVs (yet) is the relatively poor performance of current EV batteries and the high price of the few BEVs available. The only BEV with minimum acceptable e-range is the Tesla S-85, but at $100+k it is too expensive. The new Tesla X-100 may be the first practical BEV if the price can be reduced to around $50K. Here again, the availability of ultra quick charge stations will be a determining factor.

Our sole Hydro electricity producer is a 'Crown Corporation' and belongs to all people living in the Province. The 45,000+ megawatt installed produce a net profit of about $3.5B to $4.0/year. About 50% is returned to the Provincial government as dividend.

Windmills (about 2,000 mega-watt going to 4,000 mega-watt) are privately own but are heavily subsidized by the Federal-Provincial governments and Hydro Quebec. Hydro is forced to pay about $0.09/kWh for wind power and toresell it with a 50% loss. That's what had to be done to sell e-power south of the border because hydro-power was classified by States side customers as not green enough? (Please do not laugh)..

Jus7tme

>>The only reason we do not use PHEVs today is the current lack of appropriate charging facilities. This is difficult to accept in an area with a huge surplus of clean, very cheap Hydro electricity?

Well, Harvey, I'm repeating myself, but you know what the real answer is: You should be using your so-called "surplus" of hydropower to displace fossile electrical power in the rest of of the grid. You should NOT use it to charge electric cars.

>>J7t...my wife drives a new Prius III HEV and I'll probably buy a 2014 Camry Hybrid HEV late this fall.

Prius is excellent, stick with that one. Camry Hybrid is so-so. If you are looking for a hybrid sedan with some legroom, consider the Jetta Hybrid instead. It is rated at 42/48 mpg but you can easily get 50mpg overall by driving carefully.

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