Dual-fuel internal combustion engine

Abstract

A dual-fuel internal combustion engine including a regulating device for regulating the internal combustion engine, at least one piston-cylinder unit, at least one fuel injector for a gaseous fuel, which is assigned to this piston-cylinder unit, at least one gas supply device for gaseous fuel, which is assigned to this piston-cylinder unit, whereby the regulating device has a pilot operating mode in which the liquid fuel is introduced as a pilot fuel, whereby the regulating device in pilot operating mode has a transient mode in which, in an expansion phase of the piston-cylinder unit, the piston-cylinder unit is supplied with liquid fuel by the fuel injector.

Claims

1. A dual-fuel internal combustion engine, comprising: a regulating device for regulating the internal combustion engine, a piston-cylinder unit, a fuel injector for a diesel fuel, coupled to the piston-cylinder unit, and a gas supply device for gaseous fuel, coupled to the piston-cylinder unit, wherein the regulating device has a pilot operating mode in which the diesel fuel is introduced as a pilot fuel injection by the fuel injector to initiate combustion of gaseous fuel supplied to the piston-cylinder unit by the gas supply device, wherein the regulating device in the pilot operating mode has a transient mode in which, in an expansion phase of the piston-cylinder unit, the piston-cylinder unit is also supplied with an expansion phase injection of the diesel fuel by the fuel injector while heat is released from the combustion of the gaseous fuel, wherein the expansion phase injection occurs after peak heat release.

2. The internal combustion engine according to claim 1 wherein, in the pilot operating mode, the regulating device is configured to switch from a steady-state operating mode to the transient mode when a current load requirement changes beyond an absolute threshold value.

3. The internal combustion engine according to claim 2 wherein, in the pilot operating mode, the regulating device is configured to switch from the transient mode to the steady-state operating mode when approaching a new load requirement up to a predetermined distance.

4. The internal combustion engine according to claim 1, wherein the internal combustion engine is operated in lean operation with the gaseous fuel and the diesel fuel of the pilot fuel injection providing a combustion air ratio lambda of 1.7 to 1.8.

5. The internal combustion engine according to claim 1, wherein the internal combustion engine is coupled to a stationary platform.

6. The internal combustion engine according to claim 1, wherein the internal combustion engine is in a marine vehicle.

7. A method for operating a dual-fuel internal combustion engine, comprising: supplying gaseous fuel to a piston-cylinder unit of the internal combustion engine; during a steady-state phase, introducing diesel fuel to the piston-cylinder unit as a pilot fuel injection before top dead center of an expansion phase of the piston-cylinder unit to initiate combustion of the gaseous fuel; and responsive to operating in a transient phase, introducing the diesel fuel to the piston-cylinder unit as the pilot fuel injection and also as an expansion phase injection in the expansion phase of the piston-cylinder unit while heat is released from combustion of the gaseous fuel.

8. The method according to claim 7, further comprising, responsive to the operation in the transient phase, changing a position of a wastegate and/or a compressor bypass in a direction of a smaller opening.

9. The method according to claim 7, wherein the steady-state phase includes a current load demand changing by less than an absolute threshold value and the transient phase includes the current load demand changing beyond the absolute threshold value.

10. The internal combustion engine according to claim 1, wherein the regulating device in the pilot operating mode has a steady-state operating mode in which, in the expansion phase of the piston-cylinder unit, the piston-cylinder unit is not supplied with the expansion phase injection of diesel fuel by the fuel injector.

11. The internal combustion engine according to claim 1, wherein the regulating device, in the pilot operating mode, supplies gaseous fuel to the piston-cylinder unit from the gas supply device.

12. A system for a dual-fuel internal combustion engine, the system comprising: a piston-cylinder unit; a fuel injector for injecting a diesel fuel to the piston-cylinder unit; a gas supply device for supplying gaseous fuel to the piston-cylinder unit; and a regulating device configured to: supply gaseous fuel to the piston-cylinder unit via the gas supply device; during a steady-state phase, introduce diesel fuel to the piston-cylinder unit, via the fuel injector, as a pilot fuel injection before top dead center of an expansion phase of the piston-cylinder unit in order to initiate combustion of the gaseous fuel; and responsive to operating in a transient phase, introduce the diesel fuel to the piston-cylinder unit, via the fuel injector, as the pilot fuel injection and also as an expansion phase injection in the expansion phase of the piston-cylinder unit while heat is released from the combustion of the gaseous fuel.

13. The system of claim 12, wherein the regulating device is configured to introduce the diesel fuel as the expansion phase injection by commanding diesel fuel injection via the fuel injector after top dead center of the expansion phase of the piston-cylinder unit.

14. The system of claim 12, wherein, during the steady-state phase, the piston-cylinder unit does not receive the expansion phase injection.

15. The system of claim 12, wherein the regulating device is further configured to, responsive to the operation in the transient phase, change a position of a wastegate and/or a compressor bypass in a direction of a smaller opening.

16. The system of claim 12, wherein the steady-state phase includes a current load demand changing by less than an absolute threshold value and the transient phase includes the current load demand changing beyond the absolute threshold value.

17. The system of claim 12, wherein the gas supply device comprises a port-injection valve.

18. The system of claim 12, wherein the gas supply device comprises a gas mixer positioned upstream of a compressor of a turbocharger.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention are explained in more detail with reference to the figures. The drawings in detail:

(2) FIG. 1 shows a diagram of an internal combustion engine,

(3) FIG. 2A, 2B show diagrams of an injection rate and a heat release rate over the crank angle in steady-state operating mode (FIG. 2A) and in transient mode (FIG. 2B)

DETAILED DESCRIPTION

(4) FIG. 1 shows schematically an internal combustion engine 1 with a piston-cylinder unit 2 and a fuel injector 3 for injecting liquid fuel. Only one piston-cylinder unit 2 is shown by way of example. In practice, generic internal combustion engines have a plurality of piston-cylinder units 2.

(5) A regulating device 5 can regulate the quantity of liquid fuel supplied to the piston-cylinder unit 2 (via the fuel injector 3) or the supplied quantity of gaseous fuel (via a gas supply device 4). Signal lines are indicated by dashed lines. In the interest of clarity, not all signal lines leading to the regulating device 5 are shown.

(6) Exhaust gases from the piston-cylinder unit 2 flow to an exhaust-gas turbine 8 of a turbocharger 7. A compressor 9 is connected to the exhaust-gas turbine 8. In the exemplary embodiment shown, a gas supply device 4 is arranged downstream of the compressor 9. At this point, the gas supply device 4 may be designed e.g. as a port-injection valve for the cylinder-specific metering of gaseous fuel.

(7) In one variant, the gas supply device 4 is arranged upstream of the compressor 9. At this point, the gas supply device 4 may be designed e.g. as a gas mixer.

(8) The internal combustion engine 1 or the regulating device 5 is configured such that, in the expansion stroke (expansion phase) of the piston-cylinder unit 2, additional liquid fuel can be injected by the fuel injector 3.

(9) In this phase, the piston 6 of the piston-cylinder unit 2 is already beyond the top dead center and the risk of knocking is thus greatly reduced.

(10) In practice, the safe distance (how early the injection may occur after the top dead center) to the knock limit is determined by experiments. The safe distance depending on the load can be stored e.g. as a look-up table in the regulating device.

(11) The distance to the knock limit also depends on the quality of the gas used as the gaseous fuel. In particular in marine applications, the gas quality can change due to demixing in the entrained gas. A routine may be provided to determine the distance to the knock limit.

(12) The additional introduction of energy in transient mode in the form of liquid fuel in the expansion phase also causes, in addition to a higher power delivery (and thus directly increased torque), increases the enthalpy of the exhaust gas by extending the pressure phase in the piston-cylinder unit 2. Thus, more energy reaches the exhaust-gas turbine 8 of the turbocharger 7, and the compression power of the turbocharger 7 increases faster, which in turn allows a gas supply to follow faster.

(13) An optionally higher fuel consumption and reduced efficiency when driving through the transient phase is accepted.

(14) By injecting the liquid fuel in the expansion phase, only a small increase in NOx emissions can be observed since, in this period, there are temperature and pressure conditions in which barely any NOx is formed.

(15) Embodiments of the invention are particularly suitable for a lean operation with a combustion air ratio lambda of e.g. 1.7 to 1.8. Even after combustion of a lean mixture with high excess air, a sufficiently high content of oxygen for oxidation of the liquid fuel is present. This residual oxygen content is also the limiting factor for the quantity of additionally injected liquid fuel.

(16) As an additional measure, the residual oxygen content in the at least one piston-cylinder unit 2 can be increased in the short term by a wastegate 10 that can be actuated by the regulating device 5, whereby the quantity of liquid fuel that can be converted in transient mode can be increased. Instead of a wastegate 10, a compressor bypass 11 that can be actuated by the regulating device 5 could also be provided for this purpose. Actuation here means a change in the position of the wastegate 10 or compressor bypass 11 in the direction of a smaller opening. A reduced opening position increases the lambda in the short term.

(17) FIG. 2A shows an injection rate and a heat release rate plotted against the crank angle for the steady-state operating mode. The top dead center at 0 crank angle is marked by a dashed vertical auxiliary line. The peak detectable in the course of the injection rate marks the pilot injection.

(18) FIG. 2B shows the injection rate and the resulting heat release rate over the crank angle according to embodiments of the invention in transient mode. In the course of the injection rate, in addition to the peak of the pilot injection, the injection in the expansion phase can also be seen. It can be seen that, as a result of this additional injection of liquid fuel in the expansion phase compared with the pilot injection, the course of the heat release rate drops less than in the case described in FIG. 2A.

(19) The area under the heat release rate curve can be interpreted as converted heat. It is clear that significantly more energy is converted by the inventive measure of the additional injection in the expansion phase of the internal combustion engine 1 in dual-fuel operation with gas as the main fuel, which contributes to a faster response of the turbocharger 7 as stated above.

(20) This written description uses examples to disclose the invention, including the preferred embodiments, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.