DUAL-FUEL INTERNAL COMBUSTION ENGINE

Abstract

A dual-fuel internal combustion engine including at least one combustion chamber. The at least one combustion chamber is paired with an inlet valve for a gas-air mixture and an injector for liquid fuel. The internal combustion engine also includes a regulating device which is designed to carry out a switchover in a switchover mode such that a quantity of energy supplied to the at least one combustion chamber by a gas-air mixture is changed, and a quantity of energy supplied to the at least one combustion chamber by the liquid fuel and/or the time of the injection of the liquid fuel is changed. The regulating device is designed to carry out the switchover on the basis of a current load of the dual-fuel internal combustion engine, wherein the regulating device is designed to select an excess air coefficient of the gas-air mixture in the switchover mode, the coefficient being larger than a target excess air coefficient in a pilot operation.

Claims

1. A dual-fuel internal combustion engine, comprising: at least one combustion chamber, wherein the at least one combustion chamber is paired with an inlet valve for a gas-air mixture and an injector for liquid fuel; and a control device, which is designed to carry out a switchover in a switchover mode such that an amount of energy supplied to the at least one combustion chamber by a gas-air mixture is changed, and an amount of energy supplied to the at least one combustion chamber by the liquid fuel and/or the time of injection of the liquid fuel is change; wherein the control device is designed to carry out the switchover on the basis of the current load of the dual-fuel internal combustion engine; and wherein the control device is designed to select an excess air coefficient of the gas-air mixture in the switchover mode, the coefficient being larger than the target excess air number in pilot operation.

2. The dual-fuel internal combustion engine according to claim 1, wherein the control device is designed to select a longer switchover duration the higher the load is.

3. The dual-fuel internal combustion engine according to claim 1, wherein the control device is designed to select, in switchover mode, a time of injection of the liquid fuel later than the target time of injection in pilot operation.

4. The dual-fuel internal combustion engine according to claim 1, wherein the control device is designed to carry out the switchover quasi-stationary when a load change occurs.

5. The dual-fuel internal combustion engine according to claim 1, wherein the control device is designed to carry out the switchover dynamically when a load change occurs.

6. The dual-fuel internal combustion engine according to claim 1, wherein the control device is designed to lower an excess air coefficient of the gas-air mixture at a load increase above a predetermined limit value.

7. The dual-fuel internal combustion engine according to claim 1, wherein the control device is designed to increase the amount of energy supplied by the liquid fuel to the at least one combustion chamber and/or change the time of injection of the liquid fuel to a later time in the event of a load change in switchover mode above the predetermined limit.

8. The dual-fuel internal combustion engine according to claim 7, wherein the control device is designed to increase the excess air coefficient of the gas-air mixture in the event of a load change in switchover mode above the predetermined limit.

9. A method for switchover of a dual-fuel internal combustion engine, comprising: making the switchover by changing an amount of energy supplied to an at least one combustion chamber through a gas-air mixture, and at least one of changing an amount of energy supplied to the at least one combustion chamber by a liquid fuel and changing a time of injection of the liquid fuel; wherein the switchover is made on the basis of a current load of the dual-fuel internal combustion engine; and wherein during the switchover an excess air coefficient of the gas-air mixture is selected, the excess air coefficient being larger than a target excess air coefficient in pilot operation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Further advantages and details of the disclosure can be found in the figures and the related description of the figures. They are as follows:

[0035] FIG. 1 a schematic representation of a dual-fuel internal combustion engine and

[0036] FIG. 2A and 2B diagrams that show the switchover strategy.

DETAILED DESCRIPTION

[0037] FIG. 1 shows schematically a dual-fuel internal combustion engine according to the disclosure. It has four combustion chambers B1 to B4, which can be supplied with liquid fuel, in this case diesel, via the injectors I1 to I4.

[0038] To create the gas-air mixture, a central gas mixer GM is provided, which is connected to an air supply L and a gas reservoir G, e.g. a tank. The gas-air mixture produced in the central gas mixer GM is fed to the combustion chambers B1 to B4 via a gas-air mixture supply R. Downstream of the gas mixer GM, a compressor V of a turbocharger (mixed-charged internal combustion engine) is also provided. However, the gas mixer GM could also be arranged downstream of the compressor V in the air supply (air-charged internal combustion engine). The number of combustion chambers B1 to B4 is purely exemplary.

[0039] Embodiments of the disclosure can be used in dual-fuel internal combustion engines with 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22 or 24 combustion chambers. Reciprocating piston engines can be used, i.e. the combustion changes are arranged in piston cylinder units.

[0040] Embodiments of the disclosure can, in an embodiment, be used in a stationary internal combustion engine, for marine applications or mobile applications such as so-called non-road mobile machinery (NRMM), in an embodiment, as a reciprocating piston engine. The internal combustion engine can be used as a mechanical drive, e.g. for the operation of compressor systems or can be coupled with a generator to a genset for generating electrical energy.

[0041] FIGS. 2A and 2B each show two diagrams one above the other, whereby in the upper diagram the substitution rate SR (solid line) and the excess air coefficient of the gas-air mixture (dashed line) are plotted against time, and in the lower diagram each load (solid line) and the time of injection SOI (dashed line) of the liquid fuel is plotted against time. For the time of injection SOI, a higher point on the dashed curve means a later time of injection SOI, thus closer to the upper dead center for the respective cylinder in a reciprocating piston engine.

[0042] As can be seen from the graphs for the load, these examples are switchovers in the stationary operation of the internal combustion engine at relatively low (FIG. 2A) and relatively high (FIG. 2B) loads.

[0043] The substitution rate SR shown in the upper diagrams is linearly increased from a first constant value to a second constant value. This is done in the case of low load (FIG. 2A) over the indicated duration X and at high load (FIG. 2B) over the indicated period Y. As can be seen, the duration chosen with relatively low load is significantly shorter than at relatively high load. This results in time being saved in the switchover duration (except in the case of maximum load).

[0044] According to embodiments of the disclosure, during the switchover (see FIG. 2A and 2B) the excess air coefficient is increased depending on the load, which serves to prevent knocking and overfueling. The load dependency can manifest itself in the duration, during which the excess air coefficient is increased, as well as the level by which the excess air coefficient is increased.

[0045] Different actuators on the internal combustion engine can be used to increase the excess air coefficient of the gas-air-mixture. Examples are the control or regulation (of course, all combinations of the actuator examples can be used) [0046] of the gas mixer GM [0047] of the blow-off valve (not shown) of a compressor V [0048] of a wastegate (not shown) of an exhaust-gas turbine of a turbocharger [0049] of a throttle valve [0050] of a variable turbine (variable angle of turbine blades of the compressor V)

[0051] In practice, the control of, for example, a blow-off valve and/or a wastegate is preferred when compared to the control of the gas mixer GM, if fast regulation or control interventions are necessary.

[0052] In order to maintain consistent performance during a switchover with increased excess air coefficient , an increased quantity of liquid fuel is injected. The knocking tendency thereby increased is counteracted by moving the time of injection SOI to a later point (see the upper diagrams of FIGS. 2A and 2B).

[0053] However, in certain circumstances this will negatively influence the combustion efficiency. A worse combustion efficiency may result in a worse emission behavior. Due to time being saved during the switchover as mentioned previously, this can easily be accepted. All in all, this gives a faster switchover, which minimizes the risk of knocking and overfueling.

[0054] To demonstrate how to calculate the combustion efficiency, exemplary reference is made to US 2007/0000456 A1.

[0055] The situation represented in FIG. 2A and 2B refers to a stationary switchover. In a quasi-stationary switchover, interpolated load values can be provided for short time intervals. These values serve as a basis for the provision of the values for the excess air coefficient according to the principles of a stationary switchover.

[0056] Embodiments of the disclosure are not limited to the exemplary embodiments shown. Embodiments of the disclosure can be used for switchovers between all modes of a dual-fuel internal combustion engine. More than one gas mixer GM can be usedfor example, a gas mixer GM per cylinder bank with a reciprocating piston engine.

[0057] This written description uses examples to disclose embodiments, including the preferred embodiments, and also to enable any person skilled in the art to practice the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure 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.