Pneumatic nailer, fuel for pneumatic nailer and gas cartridge for pneumatic nailer

Abstract

The invention relates to the use of a composition comprising dimethyl ether (DME) as a fuel in a pneumatic nailer.

Description

[0001] Gas nailer and fuel for a gas nailer and gas cartridge for a gas nailer

[0002] Technical field

[0003] The present disclosure relates to a gas nailer, a fuel for a gas nailer and a gas cartridge for a gas nailer.

[0004] background

[0005] Gas nailers are well-known and state of the art; see, for example, US 5,197,646A. In a gas nailer, a small amount of pressurized liquefied fuel is injected into a combustion chamber, mixed with air, and the mixture is ignited by a spark. The subsequent combustion, which occurs as a deflagration, leads to a rapid pressure increase in the combustion chamber. The combustion chamber pressure drives a setting piston that shoots nails or pins into materials such as wood, steel, or concrete. The system allows for cordless, mobile use, and the technology offers fast, precise fastenings, but requires regular gas cartridge replacement and safety precautions.

[0006] Summary

[0007] Technical problem

[0008] The well-known gas nailers have several disadvantages: low thermal efficiency, hydrocarbons and soot in the exhaust gas, low (maximum) setting energy up to approximately 120 J.

[0009] The inventive task is to improve the efficiency of a gas nailer, and / or to improve its exhaust emissions, and / or to improve its power-to-weight ratio (setting energy per unit weight).

[0010] Solution: The inventive problem is solved by at least one

[0011] The invention provides means to improve efficiency. The various means according to the invention for improving efficiency are discussed below by way of example. These examples are in no way intended to be limiting, but merely to enable those skilled in the art to gain a simple understanding of the invention.

[0012] A gas nailer according to the invention, like all other gas nailers, comprises at least one combustion chamber, one cylinder, and one setting piston (including piston rod).

[0013] To drive a nail, an ignitable fuel-air mixture is produced and ignited in the combustion chamber. As a result of the combustion, the pressure in the combustion chamber increases, and the driving piston is accelerated, so that with the help of its kinetic energy a nail or bolt can be driven into a surface.

[0014] As a first means of improving efficiency, a releasable locking mechanism is considered, which initially fixes the piston in an initial position after ignition against the combustion chamber pressure (positive and / or force-fit) and only releases it when a certain static pressure has been reached at least locally in the combustion chamber as a result of combustion, which preferably corresponds to at least 50% and even more preferably to at least 80% of the static pressure that would be reached on average in the combustion chamber if the piston were not released, i.e., if the combustion proceeded approximately as a constant-volume process under otherwise identical conditions.

[0015] In conventional gas nailers, the initial confinement of the deflagrating mixture occurs primarily due to the inertia of the setting piston, resulting in a less than isochoric heat input: the setting piston is already moving while the (main) combustion is still underway. This impairs efficiency and leads to cooling of the charge during combustion, which can result in incomplete combustion and the formation of problematic, especially aromatic, hydrocarbons and soot. The soot from the (turbulent) premix flame can be partially or completely inhaled as respirable particulate matter. In principle, the confinement could be improved by using a more sluggish (heavier) setting piston, but this is not feasible due to the recoil.Soot can not only impair the function of the gas nailer, for example by fouling the spark plug, but it also poses a health hazard to the user, especially when used indoors. The same applies to hydrocarbons contained in the exhaust gas, for example with regard to benzene and other aromatics, including possibly polycyclic aromatic hydrocarbons and other soot precursor compounds. In fact, an aromatic odor is noticeable when operating commercially available gas nailers indoors. If this odor is at least partially caused by benzene, the user is smelling a known carcinogen.

[0016] Another major advantage of the locking mechanism of the setting piston according to the invention is that it allows charging without the setting piston running out of its initial stroke position or being pushed out:

[0017] For example, after locking (fixing) the piston in its initial stroke position, a miniaturized compressor can draw in ambient air, preferably through an air filter, and supply it to the combustion chamber, preferably after cooling by an (optional) intercooler. Fuel can be supplied before or after compression, or, in the case of a multi-stage compressor, also between two compression stages, to cool the intake air with the enthalpy of vaporization of the fuel. The piston itself can also be used to create a supercharge by employing it as a double-acting piston. Air can be compressed via its side facing away from the combustion chamber, stored as compressed air, and supplied to the combustion chamber as needed, thus increasing the air volume and pressure in the combustion chamber accordingly.

[0018] Parts of the device housing, preferably thermally connected to the environment, can function as pressure accumulators and intercoolers. In such embodiments of the invention, an electrically driven compressor can either be omitted, or it is only needed to compensate for pressure losses in the stored compressed air, allowing the electrically driven compressor to be smaller and lighter.

[0019] Charged nail guns with a locking setting piston according to the invention are far superior to all currently commercially available gas nailers in terms of performance and efficiency. They can even be used with typical combustion chamber volumes of approximately 250 cm³. AThree setting energies of more than 300 J can be achieved, thereby addressing applications previously reserved for powder devices and those with high-performance electromagnetic drives. In devices miniaturized by supercharging, more sophisticated pistons (e.g., regarding materials, manufacturing tolerances, seals / sealing concepts) can be used due to the smaller piston diameters. These pistons feature better seals, resulting in less blow-by and reduced tendency to tilt. Less blow-by allows for a further improvement in efficiency and, consequently, a further increase in setting energy, or an increase in the number of sets that can be performed with a given fuel supply (for a given combustion chamber volume). Supercharged setting devices with a locking setting piston according to the invention can be operated with a high excess of air (e.g., BX > 2, X > 2.5, X > 3) to reduce CO and NOx emissions.

[0020] A second means of improving efficiency lies in more effective ignition. Suitable methods include, for example, multi-point electric ignition and / or a powerful electric ignition with a high spark energy. In general terms, a powerful electric ignition is one in which no ignition delay can be observed, meaning there is no time gap between the extinction of the electric spark (i.e., the end of the discharge) and the occurrence of self-sustaining thermal combustion ("hot flame"). In a narrower sense, a powerful electric ignition is one with an ignition energy greater than 0.2 J. An extreme case of a powerful electric ignition is the direct initiation of a detonation.In terms of disclosure, the occurrence of a detonation within the mixture is particularly desirable, as this closely approximates an ideal constant-volume process and may even surpass it. Preferably, the turbulence in the combustion chamber and the ignition are coordinated such that a detonation is achieved without direct initiation; that is, such that a deflagration within the combustion chamber transforms into a detonation ("DDT"). For this purpose, passive obstacles can also be provided in the combustion chamber to generate (micro-)turbulence favorable to DDT in a known manner, such as a Shchelkin coil or perforated plates.Another way to achieve more effective ignition is to first ignite the mixture with a weak ignition source, such as a weak spark, so that a non-thermal, so-called "cool flame" is initially produced. This cool flame is then re-ignited after a time delay, for example, by means of a pressure wave, a shock wave, a flame jet, or another spark. This approach utilizes the transient self-sensitization of the mixture through an increase in temperature, the formation of free radicals, and the formation of decomposing peroxides. Dimethyl ether (su) is particularly suitable as a fuel for this purpose, as it is highly prone to both the exothermic formation of peroxides and, consequently, the formation of cool flames.

[0021] Dimethyl ether has already been proposed as a fuel component for gas nailers, but not in a way to improve exhaust emissions, but because of its technically favorable vapor pressure.

[0022] For example, DE 199 50 348 Gl teaches the use of a mixture of (A) 40 to 70 wt.% dimethyl ether, nitrous oxide and / or nitromethane, (B) 8 to 20 wt.% propylene, methyl acetylene, propane and / or propadiene and (C) 20 to 45 wt.% isobutane and / or n-butane. The fuel proposed in DE 199 50 348 Gl has a high content of hydrocarbons with carbon chains, which already leads to unfavorable exhaust gas characteristics (soot, benzene, napthalin, PAHs).

[0023] This applies in particular to highly sooty burning (singly or even polyunsaturated) hydrocarbons, which also increase the flame temperature and thus promote the formation of nitrogen oxides.

[0024] Furthermore, DE 101 46 420 C2 teaches not only the use of dimethyl ether as a fuel component but also the use of "oxygen-containing organic solvents" such as methanol, but teaches against their use according to the invention.

[0025] According to the teaching of DE 101 46 420 C2, the oxygen-containing organic solvent is to be added in such a quantity that it does not completely evaporate in the combustion chamber at a lower operating temperature. However, this leads to diffusive combustion of methanol in the "first phase" within a locally lean-burning premix flame, which is extremely unfavorable with regard to exhaust gas behavior (especially soot formation, potentially high NOx emissions). In a locally lean, hot-burning premix flame, methanol droplets evaporate. A diffusion flame exists around the methanol droplets: methanol and its pyrolysis products diffuse from the inside, i.e., from the evaporating droplet, outwards. This results in locally lean, hot-burning, nitrogen oxide-forming areas (e.g., due to propene), and rich, soot-forming areas in the vicinity of the droplets.A locally lean-burning premix flame does not mean that there is a total amount of fuel injected into the combustion chamber sufficient to create an ignitable mixture with an air-fuel ratio X > 1. This means that despite an overall stoichiometric or even rich mixture, locally lean areas can exist within the combustion chamber as long as the oxygen-containing organic solvent (e.g., DE 101 46 420 C2) has not (completely) evaporated.

[0026] In DE 101 46 420 C2, a stoichiometric or even, within certain limits, a rich mixture (X < 1) is targeted in the combustion chamber. A fuel according to the teachings of DE 101 46 420 C2 is expected to have poor exhaust gas characteristics with the formation of benzene, naphthalene, PAHs, soot, and a comparatively high amount of carbon monoxide.

[0027] A third means of improving efficiency consists of using other fuels, namely fast-burning fuels, and in particular those which form detonable mixtures with air, and whose combustion with air, at least with a sufficient excess of air, produces little or no soot, and preferably also no aromatic hydrocarbons. A fuel according to the invention consists of at least 50% (wt.) dimethyl ether (DME), and at least 80% DME or mixtures thereof with methanol and / or nitromethane.

[0028] The comparatively low lower heating value of approximately 28.8 MJ / kg initially makes the use of DME as fuel for gas nailers seem unlikely (compared to propane at 46.3 MJ / kg). However, this is less significant upon closer examination because liquid DME, compared to the light hydrocarbons typically used as fuels for gas nailers, has a much higher density at the same temperature and pressure. Furthermore, for use in gas nailers, since the fuel has a relatively low mass compared to the nailer, the volumetric energy density of the fuel is crucial, not the gravimetric density.

[0029] (The fuels commonly used so far include propane, propene, propyne, propadiene, the butanes, and the butenes, and especially mixtures of these.)

[0030] DME exhibits a particularly high laminar flame speed (which is comparatively independent of pressure) and a particularly low auto-ignition temperature. The volumetric energy density of a stoichiometric mixture of DME with air, calculated using the lower heating value, is even slightly higher at over 3.8 kJ / l than that of a stoichiometric mixture of air and propene. Consequently, mixtures of DME with air tend to detonate and deliver high heating rates in gas nailers.

[0031] DME is also particularly well-suited, due to its vapor pressure, viscosity, diffusivity, and surface tension, to enable rapid mixture formation in a gas nailer over a wide temperature range and with minimal technical effort. Partially replacing the DME with methanol results in a mixed fuel with a lower adiabatic flame temperature and, consequently, even lower NOx formation. Partially replacing the DME with nitromethane can yield an even more efficient mixed fuel, with which a higher firing energy can be achieved for a given combustion chamber volume.

[0032] Ignition boosters can also be added to the DME. Suitable boosters include, in particular, organic nitrates, nitrites, nitro compounds, nitramines, as well as peroxides including carboxylic acid peroxides and their esters, ketoperoxides, and diazo compounds. Organic compounds with particularly low auto-ignition temperatures are also suitable, such as diethyl ether, acetaldehyde, ethylene glycol dimethyl ether, and beta-myrcene.

[0033] In a narrower sense, the auto-ignition temperatures of organic compounds are to be considered “particularly low” if they do not exceed that of cetane (n-hexadecane) (202 °C under laboratory conditions).

[0034] For example, a fuel according to the invention can contain, in addition to DME, also myrole, a "substitute explosive" made of methyl nitrate and methanol. The methanol is essential for safe handling: In the event of a leak, the DME evaporates first, leaving behind a methanol-methanol phlegmatized solution in methyl nitrate, in which, under normal pressure, the methyl nitrate cannot accumulate through methanol evaporation. Preferably, the quantity of myrole added is such that, at the lowest assumed operating temperature, both components of the myrole can completely transition into the gas phase in the combustion chamber.

[0035] However, it must be emphasized that pure DME, at least with sufficiently effective ignition, is exceptionally well-suited to solving all aspects of the inventive problem: The higher efficiency results from the higher heating rate, so that the thermodynamic process approximates that of a constant-volume process (isochoric heat input followed by isentropic expansion), which is why the thermal efficiency can increase. The higher efficiency manifests itself in a higher ignition energy with an unchanged combustion chamber volume. And the exhaust gases are free of soot and aromatics. When designing the device, the person skilled in the art must ensure that undesirable pre-ignition does not occur in insufficiently cooled parts within the combustion chamber. Particular attention must be paid here to any blower and its blades, as well as the spark plugs.

[0036] The fact that DME contains oxygen, and that its stoichiometric mixture with air contains a higher fuel content compared to those of light hydrocarbons, also has advantageous aspects: namely, more effective cooling of the air through the enthalpy of vaporization of the DME fuel, and a higher partial pressure of the DME fuel in the finished mixture, which allows a thermodynamically (somewhat) more favorable initial state (higher static pressure, lower temperature) with higher cylinder filling to be achieved in the combustion chamber even without any supercharging (than with light hydrocarbons).

[0037] Brief description of the characters

[0038] Fig. 1a shows a gas nailer according to one design.

[0039] Fig. 1b shows a gas nailer according to a further

[0040] From execution form.

[0041] Fig. 2a shows a gas nailer according to another

[0042] From execution form.

[0043] Fig. 2b shows a gas nailer according to another

[0044] From execution form.

[0045] Fig. 3a-d shows a gas nailer according to a further

[0046] From the execution form. Detailed description

[0047] The revelation will be explained below using various examples, which are in no way intended to be restrictive.

[0048] In a first exemplary embodiment, symbolically represented in Fig. 1a, the gas nailer functions superficially very similarly to a conventional, commercially available gas nailer with combustion chamber 121, pneumatic chamber 122, injection nozzle 132, spark plug 133, blower 131, setting piston 111, damper 123, inlet and outlet 134, nail 140.

[0049] In contrast to known gas nailers, the setting piston has a circumferential rib 112 on its piston rod, against which a locking mechanism 100 can engage to hold the setting piston in a specific position against the pressure in combustion chamber 121. The locking mechanism 100 (e.g., with an actuator) only releases, or is only released, after a certain static pressure has been reached, at least locally, in the combustion chamber as a result of ignition by a spark plug 133. This static pressure is preferably at least 50%, and more preferably even at least 80%, of the average static pressure that would be reached in the combustion chamber if the piston were not released.The locking mechanism 100 can be actively released with the aid of an actuator A, or it can release the setting piston 111 like a slip clutch when a force threshold is exceeded, if the force on the setting piston 111 as a result of combustion in combustion chamber 121 exceeds a certain value. Release of the locking mechanism can also occur when a measured static pressure is exceeded. This allows combustion to take place at a nearly constant combustion chamber volume, which increases the thermal efficiency of the gas nailer. A stop 124 can be assigned to the circumferential rib, for example, to fix the setting piston. Fig. 1b shows a further developed variant of the gas nailer from Fig. 1a. In this variant, the locking mechanism of the setting piston is used to enable charging of the gas nailer.During the setting process, the combustion chamber pressure drives the piston in the image to the right, thereby reducing the volume of chamber 122. This causes the pressure there to rise until check valve V3 opens. This supplies compressed air to a compressed air reservoir 143 of the device, which may also include or be connected to a cooler 144. The compressed air reservoir 143 can also be supplied with the aid of a compressor 142. Ambient air is always drawn in through an air filter 141. After a nail or bolt 140 has been set, or in the event of a mis-setting, the setting piston 111 (which, incidentally, in Fig. 1b, unlike in Fig. 1a, has a circumferential groove instead of a circumferential rib) can be reflected by an air cushion remaining in chamber 122, returning to its original position, i.e., moving to the left in the image. This creates a negative pressure in room 122 compared to the ambient pressure.Consequently, check valve V6, which can be designed as a reed valve, opens and allows air filtered by filter 141 to enter chamber 122. In the piston position shown in Fig. 1b with the piston locked, the desired boost can be achieved by opening inlet valve V2. An associated exhaust valve is not shown. Valve VI allows ambient air filtered by filter 141 to be supplied to the combustion chamber before it is boosted, provided that a negative pressure exists in combustion chamber 121 relative to the ambient pressure, at least temporarily.

[0050] Overall, the cycle resembles a modified Otto cycle with isothermal compression and delivers a much higher efficiency than conventional gas nailers without compression, even at low compression ratios.

[0051] In a second exemplary embodiment, symbolically represented in

[0052] In Fig. 2a, ambient air is completely or partially dispensed with. Instead, the gas nailer has at least one first fuel reservoir 251 and at least one first oxidizer reservoir 252, both of which are pressurized. Optionally, pumps 261 and 262 are provided to further increase the pressure; these can be, for example, designed as magnetic pumps or driven by an electric motor, e.g., with motor 263. Pressure accumulators 271 and 272 are connected to the high-pressure sides of the pump(s). To drive a nail, fuel and oxidizer are injected into combustion chamber 230 by means of injectors 281 and 282 and ignited there by means of a spark plug 222. The injectors 281 and 282 can be designed as separate components or combined in a mixing nozzle, e.g., in a so-called pintle injector. It is strongly preferred that only a small amount of substance is injected in a pre-injection initially, and a main injection only takes place if, for example,Combustion has been detected with the aid of a manometer 221. Alternatively or additionally to a manometer, the position of the setting piston 210 can also be observed over time to determine whether combustion has started. In the gas nailer according to the exemplary embodiment, the process is less a constant-volume process and more a type of diesel cycle (with a more isobaric heat input). Due to the very high possible (maximum) combustion chamber pressures and expansion ratios, very high efficiencies are nevertheless achievable. The entire arrangement is preferably based on powder-operated stud setting devices and is particularly suitable when very high setting energies (e.g., > 150 J) are required.Furthermore, the fuel and oxidizer feed pumps 261 and 262 can also be driven by a pneumatic motor, for example in the form of one or more pneumatic cylinders, whereby the pneumatic motor(s) can be driven by the difference between the combustion chamber pressure and the ambient pressure, i.e., by combustion chamber gas. Fig. 2b shows this schematically: Line 290 is connected on one side to the combustion chamber and on the other side to the pneumatic motor 263 located there. The exhaust from the motor 263 is via line 291 to the environment. It is known from powder devices (PAT) to use the pressure of the powder gases for piston recirculation and cartridge feed in a similar way. In this case, the pressure of the combustion gases is used alternatively or additionally for pumping the operating fluids and increasing their pressures.In contrast to the figures, a single, decomposable operating fluid can also be used instead of two operating fluids (fuel and oxidizer). This can be actively ignited in the combustion chamber, catalytically decomposed, or both. Suitable monergols include, for example, highly concentrated, preferably stabilized, aqueous solutions of hydrogen peroxide, especially those with a weight fraction >67% H₂O₂. Suitable catalysts for the rapid decomposition of hydrogen peroxide are known, in particular, from the so-called Walter process. The decomposition of H₂O₂ yields only oxygen and water, and is therefore environmentally friendly and poses no risk to the user from toxic substances.

[0053] In a third embodiment, symbolically represented in Fig. 3 a - d, the gas nailer according to the invention has a cylinder which is divided into two pneumatic chambers 1 and 2 by a piston. Initially, both chambers are filled with a mixture. Ignition of the mixture in the front, i.e., in the initially smaller pneumatic chamber 2 located closer to the nail, causes the piston to accelerate away from the nail, and the mixture in the initially larger, rear pneumatic chamber 1 is compressed (see Fig. 3 b). According to the invention, compression ignition (HCCI) can therefore occur in chamber 1 (see Fig. 1 c), whereby the subsequent combustion can proceed extremely rapidly, thus approximating a constant-volume process (i.e., isochoric heat input) in chamber 1. Preferably, an exhaust valve (not shown) is opened on pneumatic chamber 2 before compression ignition takes place in chamber 1.The compression ignition in chamber 1 is followed by a rapid reversal of the direction of movement of the setting piston (see Fig. 1c). This is the actual working stroke, in which the setting piston moves towards the nail, and in which the setting piston can complete a longer stroke than before during compression.

[0054] With regard to the working gas in chamber 1, this heat engine can exhibit a high compression ratio, a nearly isochoric heat input, and a higher expansion than compression ratio (similar to an Atkinson cycle). It necessarily follows that the gas nailer can achieve a particularly high efficiency, at least with respect to the mixture burned in chamber 1, which, with the combustion chamber volumes typical for gas nailers, can easily exceed 45% even under lossy real-world conditions.

[0055] Another aspect of the exemplary embodiment is that HCCI combustion allows very lean mixtures, and the ignition energy can be adjusted over a wide range by adjusting the injection quantity.

[0056] Finally, it is explained how manufacturers of gas nailers, for example, can proceed to improve their exhaust gas behavior according to the invention:

[0057] To this end, they replace the previously used fuels based on light hydrocarbons with a fuel according to the invention based on dimethyl ether. The chemical compatibility (with the fuel according to the invention) must be taken into account, particularly of the foil pouches of the gas cartridges, but also of all seals that come into contact with the fuel in the device or cartridge. If necessary, different foils and / or seals must be used than before. According to the invention, foil pouches made of metal foil or a metallized laminate are generally suitable.Among the polymer films, those made of FEP (fluoroethylene propylene) coated polyimide are particularly suitable: Polyimide ("KAPTON") has excellent mechanical properties and is resistant to both pure DME and all fuels according to the invention; the same applies to the thermoplastic FEP, which ensures the weldability of the films required for the production of the bags.

[0058] Furthermore, the injection quantity is preferably adjusted to the new fuel, i.e., increased. Depending on the system, this can be accomplished on the gas nailer itself, or by appropriately adjusting the metering valves of the gas cartridges. To achieve particularly favorable exhaust emissions, the injection quantity can be measured to create an excess of air in the combustion chamber, preferably a slight excess of air, especially in the range of 1 < X < 1.5, more preferably 1 < X < 1.3, more preferably 1 < X < 1.25, and even more preferably 1.1 < X < 1.25. In other words, there should be no stoichiometric air-fuel ratio (X=l), and certainly no rich mixture, but rather an excess of air, i.e., overall (relative to the entire combustion chamber) a lean mixture.

[0059] One challenge in implementing this invention lies in the tendency of DME / air mixtures to form cool flames. When using pure DMEs as fuel, there is a possibility that a weak spark in the combustion chamber will initially produce a cool flame. The resulting (comparatively small and slow) pressure increase will then move the setting piston before rapid thermal combustion ("hot flame") with an abrupt pressure rise begins. In this case, expansion can start prematurely, shifting the cycle towards a constant-pressure cycle, which can significantly reduce the thermal efficiency of the gas nailer. This problem can be addressed by using a stronger ignition or by a releasable locking mechanism for the setting piston. Alternatively or additionally, the fuel can be modified:

[0060] As an additive, methanol can interrupt the radical chain reactions that sustain the cool flame in DME / air mixtures, particularly by scavenging OH radicals. Consequently, adding methanol to DME also increases its auto-ignition temperature (and octane rating) and can therefore prevent undesirable pre-ignition or misfires.

[0061] Suitable mixtures include, for example, 95 mol% DME + 5 mol% MeOH and 90 mol% DME + 10 mol% MeOH.

[0062] Gas nailers typically rely on mixed lubrication to prevent premature wear. This means that lubricant, such as synthetic motor oil, is added to the fuel. This is problematic because the incomplete combustion of lubricants, especially conventional motor oils, is known to produce toxic reaction products.

[0063] Pure DME is far more polar than the light hydrocarbons previously used as gas nailer fuel, and liquid DME is infinitely miscible with the highly polar methanol. Highly oxygenated lubricants, which would be insufficiently soluble in the previously used fuels based on light hydrocarbons, can be dissolved in mixtures of DME and methanol. The methanol can act as a solubilizer in this process. Highly oxygenated lubricants that can be used include ethylene glycol, propylene glycol, glycerin, polyethylene glycols, polyalkylene glycols, and polyol ester oils, as well as mixtures thereof. Particularly suitable is (dry) triacetin (glyceryl triacetate), which belongs to the polyol esters and is the simplest grease, with only limited water solubility and capable of residue-free combustion.The required amount of lubricant fs must be determined experimentally, starting, for example, from an initial volume fraction of 2% lubricant f (preferably triacetin).

[0064] The invention can thus be implemented, for example, by replacing the previous fuel with a mixture of, for example, 95 mol% DME and 5 mol% methanol (dry), to which 2 vol. % dry triacetins are added as a lubricant, the lubricant content being able to be experimentally adjusted to the requirements of the specific device.

[0065] The use of DME in the fuels of gas nailers is known per se and has been proposed, for example, in EP1093889 and CA2975317C, which, however, do not solve the present inventive problem. This is due in particular to the respective high proportions of hydrocarbons proposed, which contain carbon chains, including unsaturated hydrocarbons such as propene (propylene), which tend to form sooty flames and are also characterized by high adiabatic flame temperatures, thus promoting NOx formation and wall losses.

[0066] The fuels according to the invention are preferably dry, which is to be understood as containing at most so much water that freezing water cannot impair the function of the gas nailer at low temperatures, e.g., -15°C. To ensure this, a desiccant can be arranged in the gas cartridge, which is in constant contact with the fuel according to the invention.

[0067] A further advantage of the fuels according to the invention lies in their wide ignition limits. In particular, fuels according to the invention can burn comparatively very cleanly over a wide range of mixture ratios, e.g., in the interval 1 > X < 2. This allows for a wide degree of adjustability of the firing energy by influencing the injection quantity. For this purpose, for example, the gas nailer can be equipped with variable injection, and the injection quantity can be influenced by the user via one or more control elements. An electronic injection system can also take into account further influencing factors when controlling or regulating the injection quantity, such as, in particular, the air mass, the ambient pressure and / or the ambient temperature or the temperature of the intake air.

[0068] Alternatively, the user can change the injection quantity and thus the setting energy by replacing a gas cartridge in the nailer with one metering valve with one with a different metering valve, which delivers a different amount of fuel per stroke (by volume). Being able to adjust the setting energy via the injection quantity to the required amount offers significant advantages. For example, reducing the injection quantity as needed allows: preventing nails and bolts from being driven too deeply into yielding surfaces; dissipating less excess piston energy in the nailer; reducing mechanical stress on the nailer, also due to the lower combustion chamber pressure; reducing thermal stress on the nailer; and achieving more sets from a single gas cartridge of a given volume.

[0069] In another preferred embodiment, a fuel is obtained by first preparing a mixture of dimethyl ether with 12.9 mol% MeOH (5 wt% MeOH) and adding <2 vol% of a synthetic motor oil to it.

[0070] This composition was tested, among other things, on FISCHER FGC100 and PASLODE IM350+ injection molding machines, with the injection quantity being measured using the cartridge metering valves to create mixtures with excess air in the molding machines. At a combustion air ratio of approximately X = 1.2, an increase in the piston's kinetic energy of approximately 5.9% was measured on average, compared to standard liquid petroleum gas (LPG) cartridges. This surprising improvement can be explained by a high flame velocity and a correspondingly high heating rate: the process is more uniform in volume.

[0071] Despite the significantly lower volumetric energy density of the DME / MeOH fuel according to the invention compared to LPG, the same number of sets can be achieved as with an LPG cartridge of the same filling volume (>1100 sets with a 165mm cartridge with 80ml filling volume).

[0072] After more than 1,000 settling cycles, no soot deposits were detected on any of the devices, including the spark plug insulator. The absence of exhaust fumes was noteworthy.

[0073] Even at an ambient temperature of -15°C, all devices functioned perfectly and without misfires.

[0074] Further advantageous embodiments of the disclosure are described in A1-A21 and B1-B14:

[0075] Al. Gas nailer comprising a combustion chamber; a cylinder; a piston with a piston rod; and at least one means of improving efficiency.

[0076] A2. Gas nailer according to embodiment A1, wherein a means for improving efficiency consists of a releasable locking mechanism which is able to hold the setting piston in an initial stroke position against the combustion chamber pressure after ignition of the mixture in the combustion chamber. A3. Gas nailer according to embodiment A2, wherein the locking mechanism only releases or is only released after a certain static pressure has been reached at least locally as a result of ignition in the combustion chamber, which preferably is at least 50% and more preferably even 80% of the static pressure that would be reached on average in the combustion chamber if the piston were not released.

[0077] A4. Gas nailer according to embodiment A2 or A3, wherein the locking mechanism can be released by means of an electrodynamic actuator, an electromagnetic actuator, or a piezo actuator, wherein preferably its actuation time including a dead time is at most 10ms, and preferably at most 3ms, and further preferably at most 1ms.

[0078] A5. Gas nailer according to one or more of the embodiments A2 to A4, furthermore with a charging system, i.e. a means of increasing the amount of air and the air pressure in the combustion chamber.

[0079] A6. Gas nailer according to embodiment A5, wherein the charging is effected at least partially by means of the setting piston, by using it as a double-acting piston to generate compressed air in the cylinder on the side of the piston rod, which can be stored and supplied to the combustion chamber.

[0080] A7. Gas nailer according to example A5 or A6, wherein the charging can be effected at least partially by means of an electrically driven compressor, which preferably operates according to the displacement principle.

[0081] A8. Gas nailer according to example Al, wherein a means of improving efficiency consists in a more effective ignition than the usual weak ignition by means of a spark plug.

[0082] A9 . Gas nailer according to example A8 , wherein the more effective ignition is achieved with an electric multi-point ignition, for example by using a plurality of spark plugs per combustion chamber.

[0083] A10. Gas nailer according to embodiment A8 or A9, wherein the more effective ignition is achieved by a strong ignition by means of spark discharge, by dimensioning the ignition energy such that no ignition delay is detectable between the extinguishing of an ignition spark and the occurrence of a thermally self-sustaining combustion, or that the energy of a spark is >0.2 J .

[0084] All gas nailers according to embodiment A8 or A9 or A10, wherein the more effective ignition is achieved by means of laser ignition, corona discharge, microwave ignition or plasma ignition, which can be used alternatively or additionally to spark ignition, in the case of microwave ignition also for heating the charge.

[0085] A12. Gas nailer according to embodiment A8, wherein a means is provided to compress the charge in the combustion chamber in order to bring about compression ignition for more effective ignition.

[0086] A13. Gas nailer according to embodiment Al or one or more of the dependent claims, wherein a means of improving efficiency consists in the use of a fuel which can burn faster with air under normal conditions than the light hydrocarbons propane, propene, propyne, propadiene, butane, butene, and mixtures thereof.

[0087] A14. Fuel for a gas nailer, consisting of at least 50% (wt.) of dimethyl ether and at least 80% (wt.) of dimethyl ether or mixtures thereof with nitromethane and / or methanol.

[0088] A15. Fuel according to embodiment A14, further comprising at least one or more ignition amplifiers, wherein the ignition amplifiers include, on the one hand, organic nitrates, nitrites, nitro compounds, nitramines, as well as peroxides including carboxylic acid peroxides and their esters, as well as ketoperoxides and diazo compounds, and on the other hand, organic compounds with a particularly low auto-ignition temperature such as diethyl ether, acetaldehyde, ethylene glycol dimethyl ether and myrcene.

[0089] A16. Gas nailer according to example A1 or one or more of the dependent examples A2 - A13 with a fuel according to example A14 or A15, wherein the combustion of the mixture in the combustion chamber takes place at least partially as detonation.

[0090] A17. Gas nailer comprising an exhaust aftertreatment means, for example a catalyst or a filter, wherein the filter is preferably able to retain various nitrogen oxides and can be replaced as required, wherein the filter is, for example, designed as a filter cartridge or may comprise one.

[0091] A18. Gas nailer, in particular gas nailer according to embodiment A1 or one or more of embodiments A2 - A13 and / or A16 - A17, wherein a fuel, preferably a fuel according to embodiment A14 or A15, can be burned not only with atmospheric oxygen, but at least partially with another oxidizing agent, preferably nitrous oxide, by, for example, directing or injecting nitrous oxide from a separate gas cartridge into the combustion chamber.

[0092] A19 . Gas cartridge for a gas nailer, in particular a gas nailer according to embodiment A1 or one or more of embodiments A2 - A13 and / or A16 - A17, comprising a fuel according to embodiments A14 or A15 .

[0093] A20. Gas cartridge for a gas nailer, in particular a gas nailer according to example A18, comprising a pressure vessel and an oxidizing agent such as, for example,

[0094] Nitrous oxide.

[0095] A21. Gas cartridge for a gas nailer, in particular a gas nailer according to embodiment A18, comprising at least two pressure vessels, wherein in a fully filled state at least one of the pressure vessels contains a fuel, preferably a fuel according to embodiments A14 or A15, and at least one other pressure vessel contains an oxidizing agent, namely preferably nitrous oxide.

[0096] A gas cartridge for a gas nailer with a pressure vessel for a composition comprising dimethyl ether (DME) as fuel in a gas nailer, wherein an injection quantity of the composition from the gas cartridge into the combustion chamber of the gas nailer is measured or adjusted such that an ignitable mixture with a combustion air ratio X > 1 is produced in the combustion chamber.

[0097] The gas cartridge is equipped with a metering valve that dispenses a specific amount of fuel, the amount of which is adapted to the volume of the gas nailer's combustion chamber, so that an ignitable mixture is present in the combustion chamber.

[0098] A combustion air ratio X > 1 can be generated. The gas cartridge is thus specifically designed for a gas nailer within its specific combustion chamber volume. To achieve particularly favorable exhaust gas characteristics, the injection quantity dispensed by the valve can be dimensioned to achieve an excess of air in the combustion chamber, preferably an excess of air in the range of 1 < X < 1.5, more preferably 1 < X < 1.3, more preferably 1 < X < 1.25, and even more preferably 1.1 < X < 1.25

[0099] B2. Gas cartridge according to Bl, wherein the composition consists of DME and at least one further component selected from: other volatile organic fuels (A) containing oxygen and not exhibiting carbon-carbon bonding, other volatile organic fuels (B) , ignition enhancers, carbon dioxide .

[0100] B3. Gas cartridge according to B1 or B2, wherein the composition comprises at least 50 wt.% DME.

[0101] B4. Gas cartridge according to one of Bl - B3, wherein the composition comprises DME and optionally at least one other fuel (A) in a total quantity of at least 80 wt.% .

[0102] B5. Gas cartridge according to B3 or B4, wherein the composition consists of DME, optionally at least one fuel (A) , and the remainder of at least one further component selected from other fuels (B) , ignition enhancers, carbon dioxide, and usual impurities.

[0103] B6. Gas cartridge according to one of B3 - B5, wherein the at least one fuel (A) is selected from methanol, nitromethane, methyl formate, dimethoxymethane and dimethyl carbonate.

[0104] B7. Gas cartridge according to one of Bl-B6, wherein the at least one fuel (B) is selected from such saturated and unsaturated hydrocarbons, alcohols, aldehydes, ketones and ethers having carbon chains, in particular those with chain lengths of 2 to 5, including cyclic compounds, in particular ethene, ethyne, propane, propene, propadiene, propyne, cyclopropane, n-butane, isobutane, 1-butene, cis-2-butene, trans-2-butene, isobutene, n-pentane, isopentane, neopentane, cyclopentane, cyclopentene, cyclopentadiene, ethanol, n-propanol, isopropanol, propanal, butanal, acetone, butanone, tetrahydrofuran. B8. Gas cartridge according to one of Bl-B6, wherein the

[0105] The composition, apart from usual impurities, consists exclusively of fuels containing oxygen and lacking carbon-carbon bonds.

[0106] B9. Gas cartridge according to one of Bl - B8, wherein the at least one ignition enhancer is selected from organic nitrates, nitrites, nitro compounds, nitramines, peroxides, carboxylic acid peroxides and their esters,

[0107] Ketoperoxides, diazo compounds, tetrazenes, azides,

[0108] Diethyl ether (DEE), acetaldehyde,

[0109] Ethylene glycol dimethyl ether, myrcene and mixtures of one or more of these.

[0110] BIO. Gas cartridge according to B9, wherein the at least one ignition enhancer is selected from DEE, acetaldehyde, ethylene glycol dimethyl ether, myrcene and mixtures thereof.

[0111] Bll. Gas cartridge according to one of Bl - B9, in which the

[0112] Composition A wt.% methanol and 1 < B < 20 wt.%, preferably 1 < B < 10 wt.%, methyl nitrate as

[0113] includes ignition amplifier, wherein preferably A > 0.2 B.

[0114] B12. Gas cartridge according to Bl, in which the proportions of all components with a negative oxygen balance are adjusted in the composition such that, for the amount of fuel injected into the combustion chamber of the gas nailer, at -15°C and with homogeneous mixture formation, the partial pressures of all components with a negative oxygen balance in the combustion chamber are smaller than their saturation vapor pressures.

[0115] BIS. Gas cartridge according to a B12, further containing triacetin as a lubricant, alone or in a mixture with other lubricants and / or stabilizers and / or corrosion inhibitors, wherein the triacetin is added to the fuel of a gas nailer for the purpose of mixture lubrication. B14. Gas cartridge according to a B12, further containing an oxygenated lubricant, for example ethylene glycol, propylene glycol, glycerin.

[0116] Polyethylene glycols, polyalkylene glycols and polyol ester oils including triacetin and mixtures thereof and mixtures with known lubricants and / or stabilizers and / or corrosion inhibitors for the mixed lubrication of a gas nailer.

Claims

Patent claims 1. Use of a composition comprising dimethyl ether (DME) as fuel in a gas nailer, wherein the amount injected into the combustion chamber of the gas nailer is preferably dimensioned such that an ignitable mixture with a combustion air ratio X > 1 is produced in the combustion chamber.

2. Use according to claim 1, wherein the composition consists of DME and at least one other component, selected from: other volatile organic fuels (A) containing oxygen and not exhibiting carbon-carbon bonding, other volatile organic fuels (B), ignition enhancers, carbon dioxide.

3. Use according to claim 1 or 2, wherein the composition comprises at least 50 wt.% DME.

4. Use according to at least one of claims 1-3, wherein the composition comprises DME and optionally at least one other fuel (A) in a total quantity of at least 80 wt.% .

5. Use according to claim 3 or 4, wherein the composition consists of DME, optionally at least one fuel (A) , and the remainder of at least one further component selected from other fuels (B) , ignition boosters, carbon dioxide, and usual impurities.

6. Use according to at least one of claims 3-5, wherein the at least one fuel (A) is selected from methanol, nitromethane, methyl formate, dimethoxymethane and dimethyl carbonate .

1. Use according to at least one of claims 1-6, wherein the at least one fuel (B) is selected from such saturated and unsaturated hydrocarbons, alcohols, aldehydes, ketones and ethers having carbon chains, in particular those with chain lengths of 2 to 5, including cyclic compounds, in particular ethene, ethyne, propane, propene, propadiene, propyne, cyclopropane, n-butane, isobutane, 1-butene, cis-2-butene, trans-2-butene, isobutene, n-pentane, isopentane, neopentane, cyclopentane, cyclopentene, cyclopentadiene, ethanol, n-propanol, isopropanol, propanal, butanal, acetone, butanone, tetrahydrofuran.

8. Use according to at least one of claims 1-6, wherein the composition, apart from usual impurities, contains exclusively fuels containing oxygen and which do not have carbon-carbon bonds.

9. Use according to at least one of claims 1-8, wherein the at least one ignition enhancer is selected from organic nitrates, nitrites, nitro compounds, nitramines, peroxides, carboxylic acid peroxides and their esters, ketoperoxides, diazo compounds, tetrazenes, azides, diethyl ether (DEE), acetaldehyde, ethylene glycol dimethyl ether, myrcene and mixtures of one or more of them.

10. Use according to claim 9, wherein the at least one ignition enhancer is selected from DEE, acetaldehyde, ethylene glycol dimethyl ether, myrcene and mixtures thereof.

11. Use according to at least one of claims 1-9, wherein the composition comprises A wt.% methanol and 1 < B < 20 wt.%, preferably 1 < B < 10 wt.%, methyl nitrate as an ignition enhancer, wherein preferably A > 0.2 B.

12. Use according to claim 1, wherein the proportions of all components with a negative oxygen balance are adjusted in the composition such that, for the amount of fuel injected into the combustion chamber of the gas nailer, at -15°C and with homogeneous mixture formation, the partial pressures of all components with a negative oxygen balance in the combustion chamber are smaller than their saturation vapor pressures.

13. Use of triacetin as a lubricant, alone or in mixture with other lubricants and / or stabilizers and / or corrosion inhibitors, wherein the triacetin is added to the fuel of a gas nailer for mixed lubrication.

14. Use of oxygenated lubricants comprising ethylene glycol, propylene glycol, glycerin, polyethylene glycols, polyalkylene glycols and polyol ester oils including triacetin, as well as mixtures thereof and mixtures with known lubricants and / or stabilizers and / or corrosion inhibitors for the mixed lubrication of a gas nailer by adding them to a fuel for gas nailers according to one or more of claims 1-13.

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