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 (1) with a regulating device (5) for regulating the internal combustion engine (1), at least one piston-cylinder unit (2), at least one fuel injector (3) for a gaseous fuel, which is assigned to this piston-cylinder unit (2), at least one gas supply device for gaseous fuel (4), which is assigned to this piston-cylinder unit (2), whereby the regulating device (5) has a pilot operating mode in which the liquid fuel is introduced as a pilot fuel, characterized in that the regulating device (5) in pilot operating mode has a transient mode in which, in an expansion phase of the piston-cylinder unit (2), the piston-cylinder unit (2) is supplied with liquid fuel by the fuel injector (3).

2. An internal combustion engine according to claim 1 whereby, in pilot operating mode, the regulating device (5) is designed to switch from a steady-state operating mode to a transient mode when the current load requirement changes beyond an absolute threshold value.

3. An internal combustion engine according to claim 2 whereby, in pilot operating mode, the regulating device (5) is designed to switch from a transient mode to a steady-state operating mode when approaching a new load requirement up to a predetermined distance.

4. An internal combustion engine according to at least one of the preceding claims, whereby the internal combustion engine can be operated in lean operation with a combustion air ratio lambda of preferably approx. 1.7 to approx. 1.8.

5. An internal combustion engine according to at least one of the preceding claims, whereby the internal combustion engine is designed to be stationary, preferably as part of a genset or for driving a mechanical compressor unit.

6. An internal combustion engine according to at least one of claims 1 to 4, whereby the internal combustion engine is arranged in a marine vehicle.

7. A method for operating a dual-fuel internal combustion engine, in particular according to one of the preceding claims, whereby liquid fuel is introduced as a pilot fuel, characterized in that, in a transient phase in an expansion phase of a piston-cylinder unit (2) of the internal combustion engine, the piston-cylinder unit (2) is supplied with liquid fuel.

8. A method according to claim 7 whereby, in addition to the supply of liquid fuel, a position of a wastegate 10 and/or a compressor bypass 11 is changed in the direction of a smaller opening.

Description

[0026] The invention is explained in more detail with reference to the figures. The drawings in detail:

[0027] FIG. 1 a diagram of an internal combustion engine according to the invention,

[0028] FIG. 2a, 2b 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)

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] An optionally higher fuel consumption and reduced efficiency when driving through the transient phase is accepted.

[0039] 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.

[0040] The invention is 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.

[0041] 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.

[0042] 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.

[0043] FIG. 2b shows the injection rate and the resulting heat release rate over the crank angle according to 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.

[0044] 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.

List of Reference Signs

[0045] 1 Internal combustion engine

[0046] 2 Piston-cylinder unit

[0047] 3 Fuel injector

[0048] 4 Gas supply device

[0049] 5 Regulating device

[0050] 6 Piston

[0051] 7 Turbocharger

[0052] 8 Exhaust-gas turbine

[0053] 9 Compressor

[0054] 10 Wastegate

[0055] 11 Compressor bypass