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ExxonMobil Research files patent application on methods for expanding HCCI and other advanced combustion modes load range with fuel-alcohol blends

ExxonMobil Research and Engineering Company has filed a US patent application (#20100326387, published 30 December 2010) on methods using a wide range of fuel-alcohol blends to expand the operating envelope of engines operating in advanced combustion modes. Advanced combustion modes covered include homogeneous charge compression ignition (HCCI); premixed charged compression ignition (PCCI); low-temperature combustion (LTC) mode; or other non-traditional highly-mixed combustion modes.

As an example of the benefits, the developers say that the fuel-alcohol blend methods can expand the HCCI operating load range by about 10% to about 30% than the loads achieved when using a reference gasoline without encountering unacceptable engine noise, metallurgical stress, or elevated NOx emission levels.

The patent application is wide-reaching, with alcohols defined as including one or more compounds selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, and 2-methyl-2-propanol, and fuels defined as including (but not limited to) a gasoline, a diesel fuel, kerosene, a jet fuel, a biofuel blend (e.g. biodiesel), a renewable diesel, a Fischer-Tropsch-derived fuel, a gasoline-diesel blend, a naphtha, other fuels derived from petroleum or non-petroleum feed stocks, and any combination or blend.

The patent application covers blends of between 5% and 95% alcohol. Under the ExxonMobil application, the alcohol and fuel can be blended before introduction into the engine cylinder, or injected separately into the cylinder to form a blend containing the requisite amounts of alcohol and fuel.

In methods of the invention described in the patent application, the use of the fuel-alcohol blends to expand the load range reduces or eliminates the need for exhaust gas recirculation (EGR), variable valve timing (VVT), negative valve overlap (NVO), rebreathing, multiple fuel injection, and inlet cylinder pressure boosting. According to the filing and the testing referenced within, the approach shows:

  1. significantly reduced peak NOx emission levels;
  2. prolonged ignition delay;
  3. delayed and broadened HTHR (high-temperature heat release); and
  4. reduced maximum rates of pressure increase during HTHR.

HCCI is of great interest because it can combine the low-NOx exhaust emissions of gasoline engines with three-way catalysts with the high thermal efficiency associated with diesel engines.

HCCI combustion results from the spontaneous auto-ignition at multiple points of thoroughly mixed fuel-air charge throughout the volume of the charge gas. HCCI combustion typically occurs in two stages: a low-temperature heat release (LTHR) occurs first, followed by a high-temperature heat release (HTHR). Broadening LTHR and HTHR, and reducing the maximum rate of pressure increase during LTHR and HTHR, increases the operating range of a HCCI engine.

Despite that being well known, it is still difficult to operate in HCCI mode over a wide range of loads:

  • combustion phasing (the timing of auto-ignition) is inherently difficult to control;
  • the rapid rate of heat release by a HCCI engine as its load increases can lead to mechanical and noise problems;
  • with rapid combustion, the maximum rate of pressure rise limits the ability of HCCI engines to achieve medium and high loads;
  • HCCI is sensitive to fuel composition; and
  • fuels often do not auto-ignite at low loads.

Although EGR and VVT help to control the combustion heat release, rate of pressure rise, and NOx emissions of HCCI and other IC engines, each of these design options has its detriments, the ExxonMobil researchers noted. External EGR leads to a slow response rate since EGR gases must flow through the exhaust and EGR system. External EGR also requires substantial heat dissipation; EGR must often be cooled prior to introduction into the engine.

Further, they said, to achieve high load performance with EGR, a larger engine size is needed (due to the displacement of air by EGR), which leads to a loss of efficiency and power. While internal EGR strategies using VVT have faster response rates, these valve strategies contend with delayed intake valve closure time, which also decreases power and efficiency.

In a set of combustion experiments referenced in the application, the researchers demonstrated that including more than 10% by volume of ethanol in gasoline significantly improved the combustion performance of the fuels studied.

The data shown...demonstrate that there is a longer time interval between the low and high temperature heat release points for the fuels containing more than 10% ethanol when compared to a fuel without ethanol that has about the same (RON+MON)/2 value. This longer time interval probably provides an opportunity for some hot reactive gases to mix uniformly in the cylinder before the main combustion event and the presence of such reactive gases could assist with combustion phasing or auto-ignition in challenging environments. Thus, the unusual combustion characteristics of the processes of the invention could also enable engine designers to better optimize injection timing.

The researchers also found that the use of 15% or more ethanol reduced cycle average peak NOx levels by about 86-89% at 87 (RON+MON)/2 and 14% at 90 (RON+MON)/2.

While both sets of fuels at lower and higher octane levels saw significant NOx reduction, the result for the 87 (RON+MON)/2 fuel is an impressively large reduction. It is theorized that at the lower octane number, use of the non-ethanol fuel results in a not completely homogeneous fuel/air mixture. This can lead to less efficient combustion, increased peak combustion temperatures, and locally hot zones. NOx formation is very temperature-dependent, and tends to increase significantly with increasing peak combustion temperatures. It is believed that ethanol delays combustion long enough to significantly improve the homogeneity of the fuel mixture, thereby reducing both combustion temperatures and NOx levels. The fact that the NOx level decrease is smaller with the higher octane fuels supports this conclusion. With the higher octane base fuel (Base 90), the HTHR50 is already noticeably delayed at 26.1 msec. A further delay of HTHR50 to 35.5 msec in Fuel 90-20 does not impact the homogeneity nearly as much as with the lower octane fuel set, where the Base 87A HTHR50 is only 16.2 msec.

Resources

  • Yao et al. (2008) An investigation on the effects of fuel chemistry and engine operating conditions on HCCI engine (SAE 2008-01-1660)

  • et al. (2007) Experimental study and chemical analysis of n-heptane homogeneous charge compression ignition combustion with port injection of reaction inhibitors, Combustion and Flame 149 261-270 doi: 10.1016/j.combustflame.2007.01.002

  • Shibata, et al. (2005) Correlation of Low Temperature Heat Release with Fuel Composition and HCCI Engine Combustion (SAE 2005-01-0138)

Comments

JC

A patently ridiculous application for the exclusive rights and royalties to the concept of alcohol blended fuels in non-stoichiometric engine applications. Dozens of research labs, including MIT, have been working on this for years, and ExxonMobil thinks they can own the entire field because they've got the deepest wallets. What's next? A patent application on chicken soup?

SJC

It is a patent application and not a patent. You can make the existence of a patent application known if you wish, or keep it confidential. I hope they do not grant this application, they grant way too many for way to long a period of time...IMO.

Account Deleted

spending a lot of money on fuel is not the way to go for energy sustainability and pollutant prevention.

Instead, the way heat being converted into kinetic energy in an engine needs a major overhaul.

SJC

Every time you convert energy, energy is lost. Going from chemical energy, to heat energy, to mechanical energy is just that. Going from chemical energy to electrical energy to mechanical energy is similar. Going from chemical energy to mechanical energy would eliminate one step, but I see no way that can be done.

Only 1% of the energy in gasoline goes to moving the driver down the highway. That seems like a low number to sustain over millions of drivers. We should ask ourselves what and whom we are transporting and is there another way. Telecommuting is using electrons instead of gasoline, but until out society sees the benefits of that, we will continue to use more imported oil.

Account Deleted

converting fuel's chemical energy into heat is not a problem at all because the combustion efficiency is approaching 100%.

Converting heat into kinetic is a real problem and yet billions of dollars are spent on the portion where chemical energy conversion into heat.

Funny thing is with combustion efficiency already so high, so many engine people are claiming that they have increased engine efficiency by 50% just by improving fuel, spark plug, combustion chamber design, etc.

No wonder, piston engines and turbines still emits lot of exhaust heat and require extensive cooling. The focus and results are at the wrong place but the efficiency improvement "lie" appears to be at the right place.

ToppaTom

Well, if you convert chemical energy to heat energy at lower pressure you will have less available energy.

So maybe SJC and the entire auto and ICE industries are not so far off, eh?

Account Deleted

in gas turbines and piston engines, pressure difference and not temperature difference that move turbine blade or pistons. Unfortunately, a lot of thermal energy is just wasted without having a chance to contribute in raising the pressure.

If you want to find a solution to the world's energy problem, find a cooling medium that is far better than nitrogen in absorbing the combustion heat. Once the cooling medium absorbs the heat, it will automatically expands to move either the turbine or piston to do work.

jmeyerco

An effective way to improve the performance of ethanol-fueled engines is to cool the charge with an effective premixing intake manifold. The higher latency of vaporization relative to gasoline provides additional cooling to the charge and therefore improves the torque of the engine substantially.

James Meyer

Founder, PRV Performance

SJC

It seems like there are several methods to do a better job in the liquid fuel world. We continue to debate blend percentages while less than 1% of the pumps are E85 but almost 10% of the cars are becoming E85 capable.

If we have more E85 pumps or even blend pumps, it would provide more options and we could use less imported oil. Perhaps if those blend pumps could dispense E100 and there was a separate small tank for injection, this would be acceptable. These options are not offered so we do not know how many people would use them.

Fred H

This patent application is BALONEY.

Alcohol blended fuels are already common practice, and their use in a slightly modified ICE is not patent worthy.

If that patent is granted, I will file a patent application for blended BALONEY covering blends of between 5% and 95% fat, to expand the operating envelope of diners operating in advanced consumption modes.

I will call it Mobile ton.

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