Patent Grant
11261391
This disclosure relates to fuel and fuel blending agents. More specifically, this disclosure relates to fuel and fuel blending agents for internal combustion engines.
Biofuels are increasingly used to supplement conventional petroleum-derived fuels for transportation. As a renewable energy source, biofuels help to reduce dependence on fossil-fuel, mitigate greenhouse-gases emissions, and in some cases, improve air quality. Mandates for biofuels have been established around the world, requiring an even larger increase in biofuel usage in the future. Second-generation biofuels, using non-food-crop feedstocks, will contribute the major part of these increases. For example, US EPA has mandated that by 2022, 21 out of 36 billion gallons of biofuels (about 20% of total projected fuel demands) must be advanced biofuels produced from cellulosic or other non-food feedstocks.
With respect to the development of practical strategies for producing second-generation biofuels, the current practice involves feedstock pre-treatment (breaking down biomass), separation of cellulose, conversion of cellulose to simple sugars, and fermentation of sugars to alcohols. A major area of difficulty in this process is the recalcitrance of lignocellulosic biomass, which requires extensive pre-treatment of the feedstock and consequently reduces energy efficiency and increases the cost of production. One potential means of addressing this difficulty is the exploitation of natural biological mechanisms for breaking down biomass. For example, certain fungi, endophytes, naturally consume cellulose and excrete volatile organic compounds (VOC)—hydrocarbons and hydrocarbon derivatives—that may have utility as fuels. See, e.g., Griffin, M. A., Spakowicz, D. J., Gianoulis, T. A., Strobel, S. A., Volatile Organic Compound Production by Organisms in the Genus Ascocoryne and a Re-evaluation of Myco-diesel Production by NRRL, 50072 Microbiology 2010, 156: p. 3814-3829.
Ketones are prominent in the VOC streams from several different fungi see id. and Mends, M. T., Yu, E., Strobel, G. A., Riyaz-Ul-Hassan, S., Booth, E., Geary, B., Sears, J., Taatjes, C. A., Hadi, M. Z., An Endophytic Nodulisporium sp. Producing Volatile Organic Compounds Having Bioactivity and Fuel Potential, J. Petrol. Environ. Biotechnol., 2012, 3: p. 117., but their combustion chemistry and application in engines are not well understood. Furthermore, the suitability of a fuel for combustion applications depends on many properties.
In addition, to meet mandates for improved fuel economy, manufacturers are developing boosted, down-sized engines that are much more fuel efficient than current spark-ignition engines. Turbo-boosting and super-charging internal combustion engines can improve energy efficiency, but these engines require higher octane fuels, and autoignition of high octane fuel becomes a problem. Effectively increasing the compression ratio of boosted engines is also a challenge.
With their superior anti-knock properties, the compounds described herein may be used neat or as blending components with gasoline or other compounds to produce better fuels that could facilitate development of highly efficient engines, such as boosted, down-sized spark-ignition (SI) internal combustion engines, SI engines with a higher compression ratio (naturally aspirated or boosted), or other highly efficient engines that will be developed in the future. The compounds described herein may also be used as neat fuels or mixed fuels (with gasoline or other fuel compounds) in certain advanced engines, such as Homogeneous Charge Compression Ignition (HCCI) engines, or more generally in Low-Temperature Gasoline Combustion (LTGC) engines (using gasoline-like fuels), that have the high-efficiency advantages of HCCI but can operate with some level of charge inhomogeneities.
In an embodiment, an enhanced fuel for an internal combustion engine includes a majority portion of a fuel selected from the group consisting of: gasoline, diesel, alcohol fuel, biofuel, renewable fuel, Fischer-Tropsch fuel, or combinations thereof; and a minority portion of a ketone-based blending agent. The ketone-based blending agent is a C4 to C10 branched acyclic ketone, cyclopentanone, or a derivative of cyclopentanone.
In an embodiment, a method for powering an internal combustion engine includes the steps of combusting a fuel to drive a piston in a cylinder of the engine. The fuel comprises a ketone-based fuel selected from a C4 to C10 branched acyclic ketone, cyclopentanone, or a derivative of cyclopentanone.
In an embodiment, a method for powering an internal combustion engine includes, combusting a fuel to drive a piston in a cylinder of the engine. The fuel comprises a ketone-based fuel selected from a C4 to C10 branched acyclic ketone, cyclopentanone, or a derivative of cyclopentanone; and an additional fuel selected from the group consisting of: gasoline, diesel, biofuel, renewable fuel, Fischer-Tropsch fuel, alcohol fuel or combinations thereof.
The term “blending agent” is used herein to mean both agents used in large amounts and also to encompass agents added in small amounts that might be considered an “additive” in the art.
This present disclosure involves the use of a C4 to C10 branched ketone or cyclopentanone or a derivative thereof as a blending component for fuels, including, but not limited to gasoline. In an embodiment, the C4 to C10 branched ketone or cyclopentanone or a derivative thereof would be used as neat fuel or as a substantial blend with a traditional fuel (e.g. gasoline) or other fuel compounds) in spark-ignition (SI) engines that could be either naturally aspirated or using intake-pressure boost, and could use conventional compression ratios or increase compression ratios as permitted by the use of these fuels. In another embodiment, the ketone fuels (neat or in blends) may also be used for certain other types of engines, such as Homogeneous Charge Compression Ignition (HCCI) engines, or more generally, in Low-Temperature Gasoline Combustion (LTGC) engines (using gasoline-like fuels), that have the high-efficiency advantages of HCCI but can operate with some level of charge inhomogeneities. The term LTGC includes HCCI and stratified, partially stratified, and spark-assisted variants that still provide the high efficiency and low emission of HCCI, but work better over a wider operating range. See, for example, Dec, J. E., Yang, Y., Ji, C., and Dernotte, J., “Effects of Gasoline Reactivity and Ethanol Content on Boosted, Premixed and Partially Stratified Low-Temperature Gasoline Combustion (LTGC),” SAE technical paper no. 2015-01-0813, accepted for publication in the SAE J. of Engines, 2015.
As disclosed herein, research on these ketone compounds in an HCCI engine showed that they are highly resistant to autoignition. Cyclopentanone in particular, was found to be significantly harder to autoignite than gasoline or ethanol at naturally aspirated conditions, i.e. it is more resistant to engine knock. Furthermore, its autoignition showed even less enhancement with intake-pressure boosting (simulated turbocharging) than ethanol, which is the main blending compound currently being considered to improve the knock resistance of gasoline in boosted engines. The results obtained under HCCI engine conditions are also indicative of autoignition properties in traditional spark-ignition engines.
In an embodiment, two ketones, 2,4-dimethyl-3-pentanone (DMPN), also called di-isopropyl ketone) and cyclopentanone (CPN), were chosen to represent short chain (C4 to C10) branched ketones and cyclic ketones. These compounds have been observed in VOC streams produced by fungi, and can also be produced by other means, such as, for example, a fermentation process using genetically engineered microbes, which has already been shown to at least produce longer straight chain ketones. The ketone compounds can be derived by chemical processes from either biological or fossil feedstocks.
General molecular structures of the two classes of ketone compounds are shown below in formulas I and II. Formula I represents cyclopentanone or a derivative of cyclopentanone.
wherein R1, R2, R3, and R4, are independently selected from H, CH3, or CH2CH3.
Formula II represents a C4 to C10 acyclic branched ketone.
wherein each of R5 and R6 are independently selected from CH3 and any C2 to C8 alkyl hydrocarbon groups, provided that a total number of carbon atoms in the acyclic branched ketone is 4 to 10, and that at least one of R5 and R6 are branched C3 to C8 alkyl hydrocarbon groups.
For example, the branched C3 to C8 alkyl hydrocarbon groups may be selected from: CH(CH3)2, CH2CH(CH3)2, CH2C(CH3)3, CH(CH3)CH(CH3)2, C(CH3)3, C(CH3)2CH2CH3, C(CH3)2CH3, C(CH3)2CH(CH3)2, CH(CHCH3)2, C(CHCH3)2(CH3), CH2CH(CH2CH3)(CH3).
The C9 or C10 embodiment may be branched at any carbon atom along the chain in the R5 or R6 groups. The C9 or C10 embodiments may be especially useful in blends with diesel fuel.
The examples disclosed herein indicate the two ketone compounds disclosed herein have a lower autoignition reactivity than gasoline or ethanol when used in an internal combustion engine operating at normal, naturally aspirated (1 bar) intake pressure (Pin) conditions. At this Pin and a speed of 1200 rpm, the intake temperature (Tin) required to achieve autoignition in an HCCI engine with a compression ratio of 14:1 for these compounds may range from 156-175° C., such as for example, 160 to 170° C. Also, at this same Pin and speed, autoignition of both ketone compounds showed a higher sensitivity to temperature variations than gasoline or ethanol, as indicated by larger changes in CA50 for a given change in Tin.
Regarding cyclopentanone and derivatives thereof, the autoignition of cyclopentanone shows even lower sensitivity to changes in intake pressure Pin than ethanol, as indicated by its relatively small Tin reduction for a given Pin increase in the Examples. Also, its intermediate temperature heat release (normalized) showed no enhancement by Pin for the 1 to 1.8 bar pressure range examined, and it is even weaker than that of ethanol. This data indicates that these fuels should work well for boosted SI engines, because its knock propensity (propensity for autoignition) increases only very slightly with boost, which is in stark contrast to gasoline. Also, the lack of reactivity enhancement with increased Pin shows that the fuel will allow a higher compression ratio without knock (which enables higher efficiencies). Finally, higher compression ratios can be used in combination with boost, with significant benefits for efficiency. The extremely low autoignition reactivity enhancement with increased Pin also makes CPN an ideal fuel or blending agent for turbocharged spark-ignition engines to provide improvement in anti-knock properties.
The trends in the autoignition characteristics of cyclopentanone with changes in Pin, Tin, and engine speed are quite similar to ethanol, except that it has an even lower autoignition reactivity at all conditions tested.
Regarding the acyclic branched C4 to C10 ketone that was tested, 2,4-dimethyl-3-pentanone (DMPN), its autoignition is considerably more sensitive to (more promoted by) increases of Pin than ethanol. The rate of Tin reduction with increasing Pin is similar to gasoline; however, the DMPN remained less reactive than gasoline at all Pin tested (see
In addition, the lower reactivity (indicative of a higher RON) that the ketone-based compounds provide can enable engines to run with higher compression ratios (CR), which can increase efficiency and/or power density. In some embodiments, for example, it may be desirable to increase the CR and run naturally aspirated (zero boost). In some embodiments, both CR and boost may be raised. In others, the CR is not altered, but the boost is raised to higher levels. These options can be adjusted for desired performance and fuel economy, e.g. in economy vehicles, sports cars, and race cars.
As mentioned above, the compounds disclosed herein, in particular cyclopentanone and 2,4-dimethyl-3-pentanone may be recovered from the action of certain fungi on biomasses to produce streams of volatile organic compounds (VOCs). Reference may be made to the following publications for further information on this process. Mends, M. T., Yu, E., Strobel, G. A., Riyaz-Ul-Hassan, S., Booth, E., Geary, B., Sears, J., Taatjes, C. A., Hadi, M. Z., An Endophytic Nodulisporium sp. Producing Volatile Organic Compounds Having Bioactivity and Fuel Potential. J. Petrol. Environ. Biotechnol, 2012. 3: p. 117 and Yu, E. T., Tran-Gyamfi, M., Strobel, G., Taatjes, C., Hadi, M. Z., VOC Profile of Endophytic Fungi is Altered by Nature of Lignocellulosic Biomass Feedstock, submitted to Biores. Technol., 2013. These types of compounds, may also be produced by a fermentation process using genetically engineered microbes, which has already been shown to at least produce longer straight chain ketones.
The ketone compounds disclosed herein are also available from commercial sources and/or may be produced by known organic chemical techniques.
The examples herein are performed with neat examples of the ketone compounds used as fuels in an HCCI engine; however, the results indicate that the ketone compounds, can also be used neat or as blending agents in traditional fuels in internal combustion engines, such as LTGC engines in general or spark-ignition engines, such as gasoline, alcohols, or gasoline-alcohol blends. Both ketone compounds indicate they would function to reduce knocking in spark ignition engines compared to gasoline. In particular, because of its high autoignition temperature and little variance to boosted intake pressures, the cyclopentanone or derivative of cyclopentanone compounds would have excellent anti-knock qualities neat or as a blend component in a fuel for an SI engine that is naturally aspirated or boosted. Additionally, this anti-knock quality of the ketone compounds would allow for higher compression ratios in both naturally aspirated and boosted SI engines.
In an embodiment, the fuel blend comprises a majority portion of a fuel selected from the group consisting of: gasoline, alcohols (for example, ethanol, methanol, or butanol), diesel fuel, or combinations thereof, and a minority portion of a ketone-based compound. For example, the majority portion may be a blend of gasoline and ethanol, such as, but not limited to, the 10% ethanol in gasoline blends currently sold as pump gasoline in the U.S. In an embodiment, the majority portion fuel comprises 51% to 99.9% of the total fuel by liquid volume, such as, for example, 60% to 98%, or 80% to 95%, and the minority portion of the fuel is the ketone blending agent, for example, 5% to 0.01%, 20% to 5%, or 40% to 10% of the total fuel by liquid volume. In an embodiment, the majority portion fuel is present in a volume ratio with the ketone compound blending agent from 99.9:0.1 to 51:49, 95:5 to 70:30, or 90:10 to 60:40. Lower levels of the blending agent may be useful in both HCCI/LTGC and SI engines.
In an embodiment, the majority portion fuel has a research octane number (RON) of 50 to 150, such as for example, 50 to 75, 80 to 90, or 92 to 125. In an embodiment, low-cost, low-octane fuels, may have their RON raised with the ketone blending agent, so that the RON of the blend is increased to a level that is useful in conventional commercial vehicles, or to higher octane levels for boosted or higher compression ratio engines. In an embodiment, the ketone compounds may also be used as a blending agent in fuels with higher octane ratings, such as currently available pump gasolines (regular, mid-grade and premium) to create a fuel with an octane rating above (or well above) current premium gasoline. This would enable the combined fuel to be effective with new or modified engines that have higher boost capacities and/or compression ratios than are currently widely used. In an embodiment, the ketone compound is added in an amount effective to raise the RON of the total blended fuel above that of the majority portion of the fuel by an amount sufficient to allow higher compression ratios and/or boost that in current engines. From the trends shown in the examples section, it is expected that RON of the fuel blend can be raised, for example, 5% to 100% higher, such as 10% to 50%, or 15% to 30%, higher than the RON of the majority portion of the fuel. In particular, the RON of a low octane fuel could be raised much higher with a substantial portion of the ketone compound fuel blend. In an embodiment, the ketone compound is added in an amount wherein the autoignition temperature at 1.1 to 4 bar intake pressure (boosted conditions) of the total blended fuel is 5 to 50% higher than the autoignition temperature of the majority portion of the fuel. Autoignition temperature as used herein is the temperature in the cylinder at the time of autoignition in Kelvin. For example, at 2.4 bar intake pressure the autoignition temperature of the total blended fuel may be 5% to 50% higher than the autoignition temperature of the majority portion of the fuel, such as 10% to 40%, or 15% to 30% higher.
In an embodiment, the ketone compound may be mixed with diesel fuel. Unexpectedly, despite the low autoignition temperature of the compounds, which normally would be counter-productive in a diesel fuel or diesel-type compression-ignition engine, when blended with a high cetane fuel, such as diesel fuel, the ketone compounds may be helpful in small amounts, such as the blending agent amounts referred to above, to facilitate low-temperature diesel combustion, which has been shown to have benefits for significant reductions in soot and NOx emissions, and in some cases to improve engine efficiency.
In certain embodiments for SI engines and compression ignition engines, including, for example HCCI or more generally, LTGC engines, fuel blends may comprise one or more of the ketone compounds disclosed herein mixed with a fuel selected from gasoline, diesel, alcohol fuel, other compounds such as thermo-chemically produced biofuels, renewable fuel, Fischer-Tropsch fuel, or mixtures thereof. In this embodiment, the fuels are more evenly balanced by volume. For example, the ketone compound may comprise a volume percentage of 25% to 90% of the total blended fuel by volume, such as, for example, 45% to 85%, or 51% to 80% and the gasoline, diesel, or alcohol fuel is 75% to 10%, 55% to 15%, or 49% to 20% by volume of the total fuel by volume. In embodiment, the ketone compound is present in a ratio with the gasoline, diesel, or alcohol fuel from 90:10 to 25:75, 85:15 to 45:55, or 80:20 to 51:49.
The blending of the gasoline, diesel, or alcohol fuel and the ketone compound can be performed at the pump, for example, as a blending agent blended into the fuel in the underground containers at the filling station. In another example, two separate tanks at the filling station would be filled. One with majority portion fuel, e.g. gasoline or diesel, and one with the ketone compound, and they would come together and be mixed in the pump, as the vehicle is fueled.
The blending agent can also be added directly to the gas tank of a vehicle that is separately filled with fuel. It could also be blended at the supplier just prior to shipment to the filling station.
In an embodiment the total fuel or blending agent consists essentially of the ketone compounds disclosed herein as the only engine knock reducing agent, and other components that do not materially affect the anti-knock properties of the total fuel or blending agent.
In an embodiment, the total fuel or blending agent is exclusive of 3-pentanone, which is a commonly used fuel tracer for laser induced fluorescence (LIF) experiments. In an embodiment, the fuel or blending agent is exclusive of cyclohexanone, which has a low cetane number (10). In an embodiment, the total fuel or blending agent is exclusive of an amide.
The ketone fuels and blending agents described herein may be used in various internal combustion engines. The cyclopentanone or derivative thereof can also be used as a blending agent in spark-ignition engines, and has particular benefits in boosted engines, such as turbo-boosted or supercharged engines because of its high resistance to autoignition property change under boosted conditions. The data herein indicates it may be superior to ethanol because of certain properties. The branched C4 to C10 acyclic ketone may be particularly useful in non-boosted spark-ignition engines. The ketone fuels described herein may also find uses as blending agents in diesel or other diesel-type compression-ignition engines. The neat ketones may be used in HCCI engines as shown in the examples, or, more generally LTGC engines or spark ignition engines. The branched C4 to C10 acyclic ketone fuel may be especially useful in high load HCCI applications. These engines are known in the art and do not require extensive description to those skilled in the art.
This reduction in the autoignition temperature of the fuel can also allow for internal combustion engines that are designed to have an increased boost and/or increased compression ratios. For example, the CR and/or intake-pressure boost (i.e. turbocharging or supercharging) may be increased by 5% to 50%, such as 10% to 40%, or 15% to 30% higher. For example, the CR units of the engine may be increased from 8:1, 9:1, or 10:1 to 15:1, such as, for example, up to 14:1, or up to 13:1. Boost levels might be increased from 1.5 bar to 4 bar (absolute), such as 2 bar to 3 bar (absolute), or 1 bar to 2.5 bar.
A method for powering an internal combustion engine, includes combusting a fuel to drive a piston in a cylinder of the engine. The fuel comprises a ketone-based fuel selected from a C4 to C10 branched acyclic ketone, cyclopentanone, or a derivative of cyclopentanone. In an embodiment, the ketone-based fuel is a majority portion of the total fuel used in the engine. In an embodiment, the method further comprises boosting the intake pressure of the engine to 1.1 to 4 bar, such as, for example, 2.4 to 3 bar, or 2.2 bar to 2.6 bar.
A section including working examples follows, but, as with the rest of the detailed description, should not be read to be limiting on the scope of the claims.
Two ketone compounds, 2,4-dimethyl-3-pentanone (DMPN) and cyclopentanone (CPN), were systematically investigated in an example HCCI engine. Fundamental engine experiments were conducted over a wide range of operating conditions to characterize the autoignition reactivity of the two fuels, and their autoignition sensitivity to variations in temperature and pressure. These characteristics were compared with neat ethanol and conventional-gasoline results from the same facility, some of which were reported in Yang, Y., Dec, J. E., Dronniou, N., Simmons, B. A., Characteristics of Isopentanol as a Fuel for HCCI Engines. SAE Int. J. Fuels Lubr., 2010. 3(2): p. 725-741, SAE Paper No. 2010-01-2164 and Sjöberg, M., Dec, J. E., Ethanol Autoignition Characteristics and HCCI Performance for Wide Ranges of Engine Speed, Load and Boost, SAE Int. J. Engines, 3(1): p. 84-106, SAE Paper No. 2010-01-8, 2010.
HCCI engine performance was tested for the maximum loads at naturally aspirated and boosted intake pressures. Partially stratified HCCI combustion was also investigated to determine the potential of utilizing the unique autoignition properties of these fuels to improve the performance of HCCI engines. As mentioned above, the fuel autoignition characteristics here obtained from fundamental HCCI experiments are not only useful for HCCI engines, but can also be applied to understand the autoignition behavior in conventional engines, for example, to understand the effects of charge temperature and pressure on fuel anti-knock characteristics in spark-ignition engines.
The HCCI engine used for the Examples was derived from a Cummins B-series six-cylinder diesel engine, which is a typical medium-duty diesel engine.
Further specifications of the HCCI engine are listed in Table 1.
The engine was set up to allow both premixed fueling and direct fuel injection (DI). The premixed fueling system, shown at the top of the schematic in
The intake air was supplied by an air compressor and precisely metered by a sonic nozzle. For operation without EGR, the air flow was adjusted to achieve the desired intake pressure, as measured by a pressure transducer on the intake runner. For operation with EGR, the air flow was reduced and the valve on the EGR line was opened. The exhaust back-pressure throttle valve was then adjusted to produce enough EGR flow to reach the desired intake pressure. This typically resulted in the exhaust pressure being about 2 kPa greater than the intake pressure. For consistency, the back pressure was maintained at 2 kPa above the intake pressure, even when EGR was not used.
When EGR was used, an equivalence ratio based on total charge mass, rather than air alone, was used, which is called ϕin. It is defined as shown in formula I:
where F/C is the mass ratio of fuel and total inducted charge gas (i.e. fresh air and EGR), and (F/A)stoich is the mass ratio of stoichiometric fuel/air mixture for complete combustion. This provides a convenient and consistent way to compare data with the same supplied energy content per unit charge mass (i.e., the same dilution level) for operating conditions with different fuels and different EGR levels. Note that ϕm is the same as the conventional air-based ϕ when no EGR is used. For all conditions presented, the air-based ϕ is <1, so combustion is never oxygen limited.
The intake tank and plumbing were preheated to 50-60° C. to avoid condensation of the fuel or water from the EGR gases. The intake temperature was precisely controlled by an auxiliary heater mounted close to the engine. The cooling water and lubricating oil were maintained at 100° C. during the tests. All data were taken at an engine speed of 1200 rpm except for the speed sweep test.
Cylinder pressure was measured with a piezoelectric transducer (AVL QC33C) mounted in the cylinder head approximately 42 mm off center. The pressure transducer signals were recorded at ¼° crank angle (CA) increments for 100 consecutive cycles. The cylinder-pressure transducer was pegged to the intake pressure near bottom dead center (BDC) where the cylinder pressure reading was virtually constant for several degrees. Intake temperatures were monitored using thermocouples mounted in the two intake runners close to the cylinder head. For all data presented, 0° CA is defined as top dead center (TDC) intake (so TDC compression is at 360°). This eliminates the need to use negative crank angles or combined bTDC, aTDC notation.
The crank angle of the 50% burn point (CA50) was used to monitor the combustion phasing on the fly during the experiment. CA50 was determined from the cumulative apparent heat-release rate (AHRR), computed from the cylinder-pressure data (after applying a 2.5 kHz low-pass filter). The start of heat release was set at the minimum point on the AHRR curve before the main heat release peak. Computations of CA50 were performed for each individual cycle, disregarding heat transfer and assuming a constant ratio of specific heats (γ=cp/cv). The average of 100 consecutive individual-cycle CA50 values was then used to monitor CA50 and for the CA50 values reported. For cases where the pre-ignition heat release rates were of particular interest, the 10% burn point (CA10) was monitored instead. The individual-cycle based method was also used to analyze the maximum pressure rise rates from combustion and to calculate ringing intensity as described by Eng in Characterization of Pressure Waves in HCCI Combustion. SAE Paper No. 2002-01-2859, 2002. The ringing intensity was kept ≤5 MW/m2 to prevent engine knock.
A second method of computing the heat release rate (HRR) was used for detailed HRR-curve analysis. Here, the heat release rate was computed in a more refined way from the ensemble-averaged pressure trace (with the 2.5 kHz low-pass filter applied), using the Woschni correlation for heat transfer (see Heywood, J. B., Internal Combustion Engine Fundamentals. 1988, New York: McGraw-Hill) and a variable γ which updates as a function of burn fraction. In using the Woschni correlation, the main coefficient, C, and a coefficient in the gas velocity term, C2, were adjusted for each combustion condition so that the heat release rate is zero before and after the combustion. Consistent values for the C and C2 were used at comparable operating conditions. Using the ensemble-averaged pressure trace has benefits from the standpoint of reduced noise on the heat-release traces. On the other hand, it can lead to overestimated burn durations if the cycle-to-cycle variations are large. However, for the condition where this HRR analysis was applied, the phasing was fairly stable with the standard deviation of CA10 over 100 fired cycles averaging <1.2° CA and the standard deviation of the gross indicated mean effective pressure (IMEPg)<2%.
Exhaust emissions data were acquired with the sample being drawn just downstream of the exhaust plenum using a heated sample line (see
The ketone compounds used in these Examples were obtained from Sigma-Aldrich (purities: CPN≥99%, DMPN=98%). The relevant physiochemical properties for HCCI Combustion are shown in Table 2, along with those of gasoline and ethanol. Both ketones are clear colorless liquids at room temperature.
aEstimated from fuel hydrocarbon composition.
bData for isooctane.
Autoignition of the two ketone compounds were studied in a number of operating parameter sweeps in which wide ranges of engine speed, intake pressure, intake temperature, combustion phasing, and equivalence ratio were examined. Although the performance data are not reported in each case, all data for the Examples were collected under the conditions where the HCCI combustion was clean (ISNOx<0.1 g/kWh, no soot), efficient (combustion efficiency >96%, based on CO and hydrocarbon emissions), stable (COVIMEP <2%), and non-knocking (ringing intensity ≤5 MW/m2), unless otherwise noted.
HCCI combustion is initiated by the early autoignition reactions at low and intermediate temperatures, which trigger the main heat-release event. A fuel with higher autoignition reactivity will reach hot ignition sooner than a fuel with lower reactivity, for otherwise equal conditions. Therefore, combustion timing is often used to compare autoignition reactivity of different fuels in HCCI engines. Alternatively, autoignition reactivity can be compared based on the adjustments that are required to reach a prescribed combustion timing. For example, a fuel with lower autoignition reactivity would need a higher intake temperature, a higher intake pressure, or less EGR, etc., in order to give a same combustion timing as a more reactive fuel, since the autoignition kinetics are accelerated by increasing reaction temperature, pressure, and oxygen concentration, etc.
In Example 1, the HCCI autoignition reactivity of the two ketone fuels, DMPN and CPN, is compared in an engine speed vs. intake temperature (Tin) sweep. The results are shown in
At a given engine speed,
Between the two ketones, the acyclic (open chain) ketone (DMPN) requires a higher Tin, but the cyclic ketone (CPN) shows a steeper Tin drop for engine speeds >1200 rpm. The latter suggests that the autoignition of CPN is more sensitive to the temperature increase resulting from dynamic heating, which is confirmed in the Example 2 by the temperature sensitivity test.
In Example 2, a Tin sweep is performed to determine autoignition sensitivity to temperature. Temperature can affect the autoignition process and HCCI combustion in different ways due to the non-linear, and for some cases, non-monotonic effects of temperature on autoignition kinetics. For example, from
1200 rpm was considered the standard (control) speed for this example, as well as other examples disclosed herein. Accordingly, in Example 2 a Tin sweep was conducted at this speed to determine the sensitivity of hot-ignition timing, as indicated by 10% burn point (CA10), to variations in Tin (i.e. the Tin sensitivity) for the different fuels.
The stronger temperature-sensitivity of the ketone fuels suggests that their autoignition will be more susceptible to random variations in charge temperature, and thus greater cycle-to-cycle variation of their ignition timing would be expected. This is confirmed in
The origin of the temperature sensitivity of autoignition has been attributed to the magnitude of the temperature rise rate (TRR) just prior to hot ignition. For conditions producing higher TRRs, small variations in the charge temperature cause only small variations in hot-ignition timing (i.e. low temperature-sensitivity), resulting in a more stable IMEPg from cycle to cycle, whereas the opposite is true for conditions producing a low TRR. For a given combustion timing, the TRR prior to hot ignition is controlled by the heat-release rate (HRR) prior to hot ignition. This HRR is termed the intermediate temperature heat release (ITHR) rate, since it occurs at temperatures intermediate between hot ignition and the well-known early low-temperature heat release (LTHR). A higher ITHR-rate results in a higher TRR by more effectively counteracting the rate of piston-expansion cooling, thus giving a lower temperature sensitivity. Additionally, as CA50 is retarded (as in
However, pre-ignition reactions not only release heat, which raises the charge temperature and accelerates the reactions, but they also produce radical pools that help drive the reactions smoothly into hot ignition, a chemical effect. The relative importance of the thermal and chemical effects will depend on the fuel type and the specific intermediate-temperature reactions involved. Past success based on the thermal effect alone indicates that differences in the chemistry effect between fuels are small for many typical fuels. However, fuels with sufficiently different structure, such as DMPN studied here, it may be helpful to also consider chemical effects.
To this end, the ITHR and TRR of the four fuels are compared in
CPN, which has the strongest temperature sensitivity of the tested fuels, produced the lowest ITHR and consequently the lowest TRR prior to the heat release take-off at about 365° CA. Results for gasoline and ethanol are also consistent with this theory, with gasoline showing the highest ITHR and TRR and least temperature sensitivity (See
DMPN, the second most temperature-sensitive fuel, produced a relatively high ITHR and TRR, similar to gasoline and higher than ethanol, which does not fit into the above theory since it is more temperature sensitive (although only slightly so as seen in
The high temperature-sensitivity of the ketone fuels (
In Example 5, intake pressure sweeps were conducted to study the effects of intake boost (pressure) on autoignition and combustion for the ketone fuels.
In the results, gasoline showed the highest pressure sensitivity among the four fuels, which can be attributed to its paraffin constituents whose autoignition rates are known to be significantly promoted by pressure. The sweep does not extend beyond 1.8 bar for gasoline because the intake temperature at this pressure has already reached the minimum intake temperature of 60° C., selected to prevent potential fuel (and EGR water if used) condensation. DMPN showed a TBDC-reduction trend similar to gasoline, although it is somewhat less steep for Pin=1.0-1.8 bar. This might be caused by the open chain structure of DMPN which preserves some characteristics of paraffins autoignition. Since the Tin (TBDC) of DMPN is considerably higher than gasoline at Pin=1.0 bar, the Tin of DMPN does not drop to 60° C. until Pin=2.4 bar. In contrast, the slope for TBDC reduction with Pin is much lower for ethanol, and even more reduced for CPN, indicating that their autoignition chemistries are not enhanced by pressure nearly as much. As a result, the Tin of ethanol and CPN could not be reduced to 60° C. for the range of Pin tested.
The pressure effect on autoignition can also be determined from a comparison of the pre-ignition HRRs. In
The ITHR of gasoline is significantly enhanced by the pressure increase. As a result, the required Tin drops quickly as the pressure increases. On the other hand, the pressure appears to have little effect on the ITHRs of ethanol and CPN, which remain nearly unchanged from 1.0 to 2.0 bar for both fuels. This trend is consistent with their weak TBDC dependence on pressure, as seen in
The behavior of DMPN again does not align with the trends of the other fuels. The autoignition reactivity of DMPN increases significantly with pressure, as evident by the slope of the TBDC vs. Pin curve in
Further evidence of DMPN's unique autoignition chemistry is shown in
The fundamental HCCI experiments of Examples 1-7 show the autoignition characteristics of the two ketone fuels. The cyclic ketone, CPN, is a low-reactivity fuel for HCCI combustion and its autoignition shows strong temperature sensitivity and very weak pressure sensitivity. These characteristics are consistent with its ITHR, which is the lowest among either the biofuels or the gasoline fuels that were tested. Overall, the autoignition behavior of CPN is very similar to ethanol, except that it is less reactive and has a higher Tin sensitivity. This indicates it should have superior anti-knock properties when used as a blending agent for fuels used in boosted engines.
In Example 8, high-load HCCI operation with DMPN was investigated at naturally aspirated. The results for naturally aspirated operation (Pin=1.0 bar) are compared with newly obtained gasoline and ethanol data in
The high-load limit was approached by first operating the engine at a relatively stable condition, and then gradually increasing the fueling rate and retarding CA50 as necessary to prevent excessive ringing, until reaching the knock/stability limit. During this process, Tin was reduced to obtain the required CA50 retard, and no EGR was used. When the combustion was stable, CA50 was adjusted to obtain a constant ringing intensity of 5 MW/m2, which is the maximum ringing intensity that still ensures knock-free operation. Setting CA50 in this manner gives the most advanced combustion phasing without knock, and thus the highest thermal efficiency. However, lower ringing intensities, produced by additional CA50 retard, were required at some conditions to achieve sufficiently stable combustion phasing.
As
The indicated thermal efficiency of HCCI combustion is compared for the three fuels in
Despite these differences, the overall behavior of all three fuels is similar and typical of low-reactivity fuels, i.e. fuels requiring a high intake temperature, which limits the maximum IMEPg (due to a lower charge mass with the reduced density at higher temperatures) and produces relatively large amount of NOR.
The HCCI combustion performance at a significant boost pressure, 2.4 bar, was evaluated in Example 9 and the results are shown in
In Example 9, DMPN reaches a maximum IMEPg of 13.8 bar, which is very close to the maximum IMEPg for gasoline (13.9 bar) and significantly higher than that of ethanol (12.5 bar). The similar maximum loads for DMPN and gasoline are somewhat unexpected given that DMPN does not allow as much combustion retard as gasoline to limit the ringing intensity, due to its relatively low ITHR. As shown in
This additional HRR-control mechanism for DMPN is likely its high temperature-sensitivity. It is known that thermal stratification (TS) of the charge develops naturally due to heat transfer and convection. Even though the fuel/air mixtures are compositionally homogeneous, this TS will produce sequential autoignition which reduces the HRR, and thus, helps to control the pressure rise rates (PRR). However, the effectiveness of thermal stratification for HRR control depends on the temperature sensitivity of the fuel, i.e. it should be more effective for fuels with higher temperature sensitivity. In
In Example 10 a comparison of HRR of DMPN and gasoline at similar HCCI operating conditions. As indicated, Pin, Tin, ϕm, and CA50 are the same for both fuels. DMPN used less EGR due to lower autoignition reactivity.
In addition to the high temperature sensitivity, another factor enabling DMPN to reach about 14 bar IMEPg is that Tin=60° C., which is the same as gasoline. Having the same intake temperature results in similar charge densities, so that similar fueling rates can be used. In contrast, ethanol requires higher intake temperatures (>85° C.) due to its much lower autoignition reactivity at this boost pressure, which reduces the charge density and limits the fueling rate. As a result, the maximum IMEPg of ethanol is considerably lower, even though it may have a stronger temperature-sensitivity than DMPN at this Pin, and it does not use any EGR.
Other performance data based on the experiments done at boosted pressure in Examples 9 and 10 show that NOx emissions are more than an order of magnitude lower than those at naturally aspirated conditions or the US2010 NOx limit (
In summary of Examples 8-11, the results show that for Pin=2.4 bar, DMPN has autoignition behavior between that of gasoline and ethanol. Ethanol represents fuels with very low autoignition reactivity, showing low reactivity at Pin=1 bar, and increased pressure causes only a modest enhancement in its reactivity. Gasoline represents a different type of fuel; its reactivity is low at Pin=1 bar, but it is enhanced significantly by increased pressure. At Pin about 1.8 bar, the required Tin for gasoline drops to 60° C., and EGR is required at higher pressures for combustion phasing/knock control. In contrast, DMPN shows a lower reactivity at Pin=1.0 bar than either gasoline or ethanol, but its reactivity—in terms of TBDC reduction with Pin—is enhanced by pressure in a similar manner to gasoline. However, because DMPN requires a much higher Tin than gasoline at Pin=1.0 bar, its required Tin does not reach 60° C. until Pin is about 2.4 bar. At this pressure, DMPN still preserves some of the characteristics of low-reactivity fuels. For example, compared to gasoline, its autoignition is still quite temperature sensitive, which allows the naturally occurring thermal stratification to be more effective for reducing the HRR, so less CA50 retard is required to control knock. Also, since Tin=60° C. has just been reached at Pin=2.4 bar, and combustion is less retarded, DMPN requires much less EGR than gasoline. Both the more advanced CA50 and less EGR act to increase its thermal efficiency over that of gasoline. Therefore, although the CA50 of DMPN cannot be retarded as much as gasoline to allow a similar fueling rate, it reaches a similar high-load limit due to its higher thermal efficiency. For other boost pressures, which were not tested, it is anticipated that the maximum loads of DMPN and gasoline will be similar at Pin>2.4 bar. This should continue until the maximum load of gasoline becomes oxygen limited at Pin about 2.6 bar, beyond which DMPN could produce higher maximum loads with more oxygen available to support higher fueling rates. At Pin<2.4 bar, DMPN would likely produce lower maximum IMEPs than gasoline since the Tin would be higher than 60° C., which limits the charge density and therefore, the charge mass, similar to ethanol at Pin=2.4 bar in
For the open-chain ketone, DMPN, the autoignition shows strong temperature sensitivity (but less than CPN), and also fairly strong pressure sensitivity, much stronger than ethanol but somewhat weaker than gasoline. The autoignition being sensitive to both temperature and pressure is unique to DMPN, and this provides some unusual properties for its performance at high-load boosted conditions, as shown in Examples 8-11.
In summary, it was found that CPN had the lowest autoignition reactivity of all the biofuels and gasoline blends tested in this HCCI engine. The combustion timing of CPN is also the most sensitive to intake-temperature (Tin) variations, and it is almost insensitive to intake-pressure (Pin) variations. These characteristics and the overall HCCI performance of CPN are similar to those of ethanol.
DMPN shows multi-faceted autoignition characteristics. DMPN has strong temperature-sensitivity, even at boosted Pin, which is similar to the low-reactivity ethanol and CPN. On the other hand, DMPN shows much stronger pressure-sensitivity than ethanol and CPN. This pressure-sensitivity reduces the Tin requirement for DMPN as Pin increases, in a manner similar to gasoline, and it allows the same Tin=60° C. for DMPN as for gasoline at Pin=2.4 bar. At this Pin, DMPN reaches a maximum HCCI load similar to gasoline, i.e., about 14 bar IMEP. Unlike gasoline, which requires significant combustion-timing retard to prevent knock at this maximum load, DMPN allows a more advanced combustion timing because its high temperature-sensitivity causes a lower heat release rate. As a result, DMPN yields a higher thermal efficiency than gasoline at comparable loads. Accordingly, less fuel is required to do the same work, which equates to better fuel economy. Thus, DMPN also produces lower greenhouse gas emissions from the engine operation, in addition to the reduction that results from it being produced from a renewable source.
All patents, patent applications, publications, technical and/or scholarly articles, and other references cited or referred to herein are in their entirety incorporated herein by reference to the extent allowed by law. The discussion of those references is intended merely to summarize the assertions made therein. No admission is made that any such patents, patent applications, publications or references, or any portion thereof, are relevant, material, or prior art. The right to challenge the accuracy and pertinence of any assertion of such patents, patent applications, publications, and other references as relevant, material, or prior art is specifically reserved.
In the description above, for the purposes of explanation, numerous specific details have been set forth in order to provide a thorough understanding of the embodiments. It will be apparent however, to one skilled in the art, that one or more other embodiments may be practiced without some of these specific details. The particular embodiments described are not provided to limit the invention but to illustrate it. The scope of the invention is not to be determined by the specific examples provided above but only by the claims below. In other instances, well-known structures, devices, and operations have been shown in block diagram form or without detail in order to avoid obscuring the understanding of the description. Where considered appropriate, reference numerals or terminal portions of reference numerals have been repeated among the figures to indicate corresponding or analogous elements, which may optionally have similar characteristics.
It should be appreciated that the terms “a,” “an,” and “the” should be interpreted to mean “one or more” unless context clearly indicates to the contrary. The term “or” is not meant to be an exclusive “or” unless context clearly indicates to the contrary. It should also be appreciated that reference throughout this specification to “one embodiment”, “an embodiment”, “one or more embodiments”, or “different embodiments”, for example, means that a particular feature may be included in the practice of the invention. Similarly, it should be appreciated that in the description various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects may lie in less than all features of a single disclosed embodiment. Thus, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of the invention.
This application claims priority to U.S. Provisional 61/981,389, filed on Apr. 18, 2014, which is hereby incorporated by reference in its entirety.
This invention was developed under Contract DE AC04-94AL85000 between Sandia Corporation and the U.S. Department of Energy. The U.S. Government has certain rights in this invention.
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| Number | Date | Country | |
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| 61981389 | Apr 2014 | US |
