Method for a diesel engine and diesel engine

Abstract

Disclosed is a procedure to minimize NOx during varying engine loads in a 4-stroke diesel engine including at least one cylinder with a cylinder head, first piston on a connecting rod, one actuator mounted on the cylinder head and one of the actuator operated second piston lockable via a hydraulic circuit in various positions in a combustion chamber. The second piston, at the latest during the current compression stroke is actuated by the actuator and locked in the combustion chamber, where it by the first piston introduced air is compressed in a predetermined compression ratio to meet an existing engine load wherein the free operated inlet valve is brought to close the inlet stroke at a piston position where the volume of the combustion air as introduced at the end of the compression stroke gives the predetermined compression ratio and that the injector injects the stated amount of fuel.

Claims

1. A Method to minimize NOx during varying engine loads in a 4-stroke diesel engine, said engine comprising: at least one cylinder with a cylinder head, a reciprocating first piston mounted on a connecting rod, an actuator mounted on the cylinder-head, and a second piston operated by the actuator, said second piston being configured to be locked via a hydraulic circuit in various positions in a combustion chamber, wherein the cylinder head is provided with at least one outlet valve for exhaust gas evacuation, and at least one freely controllable inlet valve for the supply of combustion air, wherein at least one injector is connected to the combustion chamber for injection of fuel in said chamber, said method comprising: actuating the second piston, at the latest during the current compression stroke using the actuator, and locking the second piston using the hydraulic circuit at a position in the combustion chamber such that combustion air introduced by the piston is compressed at a predetermined compression ratio to meet a desired engine load; ending the inlet stroke by closing the freely controllable inlet valve at a piston position where a volume of the combustion air as introduced at the end of the compression stroke gives the predetermined compression ratio; and injecting an amount of fuel using the injector, the amount of fuel corresponding to the desired engine load.

2. The method according to claim 1, wherein the amount of fuel is calculated based on measured values of an air mass meter.

3. The method according to claim 1, wherein the actuating comprises actuating the second piston to move to a changed position in the combustion chamber at the latest during the compression stroke following a changed opening time for the at least one inlet valve during the preceding inlet stroke.

4. The method according to claim 1, wherein the actuating comprises actuating the second piston to move to a changed position in the combustion chamber not later than during the preceding exhaust stroke.

5. The method according to claim 1, further comprising changing the engine load from partial to maximum engine load during work strokes.

6. A 4-stroke diesel engine comprising: at least one cylinder with a cylinder head, a reciprocating first piston mounted on a connecting rod, an actuator mounted on the cylinder head, a second piston operated by the actuator, said second piston being configured to be locked by a hydraulic circuit in various positions in a combustion chamber, wherein the cylinder head is provided with at least one outlet valve for evacuation of exhaust gases and at least one freely controllable inlet valve for introducing combustion air, wherein at least one injector is connected to the combustion chamber for injection of fuel into the chamber, wherein the diesel engine further comprises an engine control system configured to: control the actuator to displace the second piston, and control the hydraulic circuit to lock the second piston at a position in the combustion chamber such that combustion air introduced by the piston is compressed at a predetermined compression ratio to meet a desired engine load; control the freely controllable inlet valve to close during the inlet stroke at a piston position where the volume of the combustion air which has been introduced and which at the end of the compression stroke gives the predetermined compression ratio, and control the injector to inject an amount of fuel which corresponds to the desired engine load.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The invention will now be described in connection to the attached drawings showing preferred examples where

(2) FIG. 1 is schematically a cross section of the upper part of an engine cylinder with the piston in its upper stroke mode at low load,

(3) FIG. 2 is schematically a cross section of the upper part of an engine cylinder with the piston in its upper stroke mode at maximum load and in which

(4) FIG. 3 is schematically a cross section of the upper part of an engine cylinder with the piston in its upper stroke mode at medium load.

(5) FIG. 1 is schematically a cross section of the upper part of an engine cylinder with cylinder head where the combustion chamber volume is adapted for small engine load and with the engine piston at its upper stroke mode after a compression stroke. In principle all the air that has been loaded under the inlet stroke is locked in said volume.

(6) FIG. 2 is schematically a cross section of the upper part of an engine cylinder with cylinder head where the combustion chamber volume is adapted for maximum engine load and the engine piston is in its upper stroke mode after a compression stroke. In principal all the air from the inlet stroke is locked in the above mentioned volume.

(7) FIG. 3 is schematically a cross section of the upper part of an engine cylinder with cylinder head where the combustion chamber volume is suitable for medium sized engine load and the engine piston in its upper stroke mode after a compression stroke. In principal all the air from the intake stroke is locked in the above mentioned volume.

(8) An engine cylinder with cylinder head 1 with a piston 2 mounted on a connecting rod 3 is shown in FIG. 1. An actuator 4, in principle the execution of patents (SE535886 C2, SE110 0435 (A1). The engine valve according to the above mentioned patent has been replaced with a piston 5 which is displaceable in a combustion chamber 7. The piston 5 can, via the signal from the engine control system, not shown here, be controlled to adopt different positions in the combustion chamber and thus vary the volume of the part below the piston wherein a substantial part of the combustion takes place when the fuel is injected through the injector 9. The different modes is locked by a hydraulic circuit 6 described in said patent. An outlet valve 8 is controlled by a camshaft or by an actuator as e.g. in said patent shown symbolically as well as an inlet valve 10 which advantageously, but not necessarily, is opened and closed by an actuator on the signal from the engine control system with a function in accordance with the aforementioned patents. An air mass meter 11 is arranged for the measurement of the amount of air supply at inlet stroke via inlet valve 10. Piston 2 shown in its upper stroke mode where it must not be allowed to reach a mechanical contact with the cylinder lock including the poppet valves 8, 10.

(9) FIG. 2 shows the piston 5 in its upper position where the combustion chamber is at its maximum and the engine can, but need not necessarily, be loaded to the maximum. Still as today more or less engine load can be charged depending on how much fuel is injected, in this case with the higher exhaust emissions of to-day. However it may be advantageous with a small recess in the piston where the piston cavity is located, i.e. in the middle of the combustion chamber.

(10) FIG. 3 is schematically a cross section of the upper part of an engine cylinder with a cylinder head where the combustion chamber volume is suitable for medium sized engine load and the engine piston in its upper stroke mode after a compression stroke. Basically all the air from the intake stroke is locked in the above mentioned volume. An interesting drive mode is when e.g. a vehicle driver suddenly presses the accelerator pedal to the bottom and thus calls for maximum engine power. During the subsequent expansion stroke the hydraulic circuit 6 locking the piston 5 in the combustion chamber 7 deactivates wherein the plunger in a few ms moves to the upper position in FIG. 2 and at the same time will the free operated inlet valve 5 at the following inlet stroke be kept open for maximum supply of air. At the compression end the appropriate amount of fuel is injected to minimize NOx. The said activities are operated by the engine control system.

(11) It should be noted that a computer-based engine control system of today is obvious and therefore need not be mentioned here how to achieve the opening and closing of the free valves and the piston 5 positioning in the combustion chamber 7 and that the injection of fuel via the injection selector switch 9 commanded by the engine control system which is also connected to the necessary sensors and sonds.

(12) It should be said that combustion will not fully take place in the combustion chamber, as corresponding the current piston cavity with the difference that the size of it can be varied depending on how much air is introduced in the inlet stroke. The combustion ceases after the piston 2 leaves its upper stroke mode and the pressure of the expanding combustion gases acts over the entire piston surface. The said variety and inlet valve opening time under inlet stroke decided by an engine control system which is presumed to exist without being shown in the figures or otherwise being detailed mentioned.