NL2004001C2 - CONTROL DEVICE AND CONTROL METHOD FOR CONTROLLING AN OTTO GAS ENGINE ON GAS FUELS. - Google Patents

Description

Control device and control method for controlling an Otto gas engine on gaseous fuels.

The invention relates to a control device and method for controlling an Otto gas engine (with or without pressure filling). Although the invention is applicable for supplying relatively rich gases of substantially constant composition such as natural gas or LPG vapor, it is particularly suitable for poor and / or compositionally fluctuating gases such as biogas.

The invention preferably replaces any conventional lambda control that may be present. Therefore, a lambda sensor is missing in an advantageous embodiment of the invention.

In particular, the invention provides a method and device with which the ignition time of an Otto gas engine can be easily adapted to the composition of the gaseous fuel supplied thereto.

The invention can be realized in a control unit which reads in the required parameters, processes it according to a certain protocol and then delivers the required control. The invention can also be applied by integrating the protocol into an already existing technique, such as a PLC or the like.

The invention can be applied to an Otto gas engine with natural carburation, but can also be applied to an Otto gas engine with gas injection.

This invention can be applied for mobile installation (for example on a truck), or for fixed installation (for example a heat-power installation for, for example, greenhouse horticulture).

The prior art already contains much basic knowledge that has been used for the present invention. Reference is made by way of example to DE3830687 (MAN) and DE102004060893 (MDE).

DE3830687 describes the calibration of the oxygen sensor in the exhaust gas system. This type of sensor has a large measuring voltage curve and a short service life, especially with aggressive fuels. In addition, this method is not suitable for highly varying fuels such as biogas, because 2 requires a different lambda for each gas composition.

DE10 2004 060893 A1 describes the adjustment of the ignition based on temperature difference. The reference temperature is determined here from the generator power. A link to the current lambda, current engine efficiency and current cooling water temperature and mixture temperature is missing, so that variation in cooling water temperature and mixture temperature is incorrectly corrected. When the lambda value is lowered, the measured exhaust gas temperature will increase, as a result of which the ignition will eventually be brought forward. A reduction in the lambda value and advance of the ignition, however, will usually lead to engine damage. With an increasing mixture temperature, the exhaust gas temperature will also increase, as a result of which the ignition will eventually be brought forward. However, an increase in mixture temperature and advance of the ignition will usually lead to engine damage.

US 6 189 523 BI is based on open loop and closed loop mapping. This is a method that only functions optimally if you know the characteristics of the fuel and the engine behaves theoretically, ie when there are no mechanical deviations. In order to be usable in practice, a reserve (safety margin) must be applied, as a result of which the engine, however, no longer runs at its best settings. Nevertheless, the risk of engine damage remains high, because the control does not signal that there is something wrong with the engine.

The article by John B. Heywood, "International combustion engine Fundamentals" in 1988, McGraw Hill international editions, 30 New York, XP007913233, ISBN 0071004998, pages 673-697, is only relevant when the properties of the fuel are known and the motor runs at the corresponding settings. With biogas, however, these parameters change continuously

In the present art, constant efforts are made to create the correct engine settings over the entire power range of the gas engine. In this connection, taking into account the government-imposed requirements for the exhaust gas composition, an optimum combustion efficiency must always be sought while avoiding factors such as engine operation disruption, detonation, skipping, etc. The invention contributes to this. to strive.

It has been found that the invention can be realized in combination with suitable control protocols which can be developed experimentally by the person skilled in the art and which can for instance be implemented with a simple PLC or equivalent. The required equipment effort is thereby very limited, so that the investment and maintenance costs are low, and the control is malfunction-resistant and therefore particularly reliable.

It has also been found that an already existing control device 15 of a gas engine can easily be converted into the control device according to the invention.

In addition, it has been found that the invention is suitable for biogas-powered engines, wherein the biogas used may contain an amount of methane gas (CH4) between 40 and 70 volume% and a 20% CO2 gas between 30 and 60 volume%.

The invention is described in more detail below on the basis of a motor operating on a poor biogas mixture (excess oxygen relative to the fuel) (so-called lean burn gas engine). However, it is to be understood that the invention is not limited to this application.

First, some background information is provided for a proper understanding of the invention.

The working area of a lean burn gas engine lies between the knock limit and the misfire limit. If the knock limit is exceeded, spontaneous ignition of the gas mixture will occur. The combustion is then uncontrolled, so that engine damage can occur. If the misfirel limit is exceeded, a loss of inflammation will occur. The resulting mechanical imbalance in the engine can also cause engine damage.

The operating point of the engine is determined by the ratio of the gas mixture (lambda) and the average effective combustion pressure. The graph of fig. 1 (vertical the pressure, 4 horizontal the lambda) shows this relationship (between lambda, combustion pressure and engine operation). With a richer mix (lower lambda), the operating point will shift towards the knock limit (horizontal). At a higher effective combustion pressure, the operating point will also shift towards the knock limit (vertical).

The optimum operating line is a line (shown in dotted lines in Fig. 1), parallel and left of the misfire boundary. The optimum operating point of the engine leads to the optimum efficiency, the lowest thermal load and the lowest exhaust emissions. This invention relates to the control method and device for finding the optimum operating point of the gas engine. The invention corrects the motor settings as a result of a change in the operating parameters.

To find the optimum operating point of the motor, the invention uses two control procedures (see Fig. 3 which shows a block diagram of the inventive control). The primary procedure (the top four blocks in Fig. 3) must find the ideal lambda, the secondary procedure (the remaining blocks in Fig. 3) must find the ideal combustion pressure.

20 The ideal lambda is found by means of an unrest measurement: In parallel operation, the generator power is measured. Generator power will temporarily decrease slightly during an ignition failure; the degree of deviation is the degree of unrest. The speed is measured during island operation. During an ignition failure the speed will temporarily decrease slightly; the degree of decrease is also the degree of unrest. The controller controls the gas flow through a controlled control valve in the gas supply. The lambda measurement / unrest measurement takes place in pre-programmed measurement periods. The control controls the controlled control valve with a pre-programmed speed to the closed position. If the misfire limit is reached, the fluctuation in power (parallel operation) or speed (island operation) will occur. The control then sends the controlled control valve to the open position at a pre-programmed speed until the fluctuation in power or speed has disappeared. The corresponding position of the controlled control valve provides the correct lambda value.

5

The ideal pressure is found indirectly by means of a temperature measurement: The optimum exhaust gas temperature of the gas engine is determined by the engine power, the mixture temperature and the engine water temperature. This optimum exhaust gas temperature is only correct if the optimum lambda value has first been reached. These three parameters are measured and then compared in the control unit in a pre-programmed table and lead to a reference temperature. The mixture temperature is preferably measured in the joint part of the inlet manifold, i.e. after an optional intercooler. The exhaust gas temperature is preferably measured in the joint part of the exhaust manifold, i.e. for a possible turbocharger. With a line engine (which after all has a single exhaust bench), a single measurement sensor for the exhaust gas temperature is sufficient; with a V-engine (which, after all, has a double exhaust bench, see fig.

2 which shows a V-motor in top view, with the position of sensors with this motor type) is preferably measured with two measuring sensors (one in each outlet bank), and an average value is determined from the two measuring signals. The measured exhaust gas temperature is compared by the control unit with the reference temperature. If the measured exhaust gas temperature is higher than the reference temperature, the control unit will advance the ignition time with a pre-programmed speed until both temperatures are equal. If the measured exhaust gas temperature is lower than the reference temperature, the control unit will leave the ignition time at a pre-programmed speed until both temperatures are equal.

It is recommended to apply the total procedure in the correct order. The correct ignition time can only be found after the correct lambda has been found. If only part of the total procedure is applied, this can lead to engine damage.

Thus, a combination of engine cooling water temperature, mixture temperature 6 and exhaust gas temperature is used for the invention. Preferably, use is not made of an oxygen sensor voltage as a reference (as with DE3830687), but a position of the gas valve is used.

EXAMPLE

Application of the invention to an Otto gas engine with natural carburation is as follows:

The gas engine draws in the air and gas via a carburetor; these gases are mixed in the carburetor. In the gas supply is a controlled control valve, which controls the gas flow to the carburetor. The resulting gas mixture is supplied, possibly via a turbocharger and an intercooler, to the cylinders of the engine block via the intake manifolds. A temperature sensor for measuring the mixture temperature is located in the joint part of the inlet manifold, so after a possible intercooler (see figure 2). The cylinders of the engine block exhaust the exhaust gases after combustion via the exhaust manifolds to a possible turbocharger and the exhaust gas system.

A temperature sensor for measuring the exhaust gas temperature is located in the joint part of the exhaust manifold, thus for a possible turbo charger.

A temperature sensor for measuring the temperature of the engine cooling water is located in the emerging cooling water pipe, as close as possible to the engine block. The gas engine has an electronic ignition system that controls the ignition voltage and the time of ignition. This ignition voltage is converted into a spark by means of the spark plugs of the gas engine, whereby the combustion in the cylinders is initiated. The electronic ignition system has a control input with which the ignition time can be influenced.

The gas engine has a gear ring, which is used for the mechanical coupling to the starter motor. A magnetic pick-up is mounted at a fixed position with respect to this tooth ring and with this magnetic pick-up the speed and the speed disturbance can be determined.

7

The generator power is measured by means of already existing inverters. These inverters determine the generator power supplied based on the measured generator voltage, generator current and cosphi. The output signal of these 5 inverters is an analog voltage in relation to the generator power supplied. The generator power and the turbulence of the generator power can be determined from this voltage.

A lambda probe is missing.

FIG. 4 shows an example of the inventive control unit with the inputs and outputs for the signals used. The six inputs concern the speed, power, temperature of the mixture, the cooling water, the outlet on the left and the outlet on the right. The two outputs relate to the position of the gas valve and the time of the ignition

Meaning of the figures in the drawing:

FIG. 1 1 knock 20 2 NOx 3 optimum operating line 4 do not ignite

FIG. 2 25 Tu outlet temperature Tm mix temperature

Claims (8)

Method for operating, using a control unit with an electronic ignition system that controls the ignition voltage and the ignition time, a movable or fixedly arranged Otto gas engine with gas injection or natural carburation to control the ignition time of the Otto gas engine to be adapted to the composition of the supplied, for example poor, gaseous fuel, for example biogas, with for example fluctuating composition, which control unit reads in the required parameters, processes it according to a certain protocol and then delivers the control required for the ignition system to substantially create the correct engine settings for optimum combustion efficiency without engine damage in the entire power range of the gas engine, the control unit applying two control procedures, a primary procedure for finding the ideal lambda, a secondary procedure for finding the ideal 20 combustion pressure, and from the result of both procedures, controls the ignition system, the primary procedure comprising a motor trouble measurement, and the secondary procedure a determination or approximation of a reference temperature by measuring the engine power, the mixture temperature and the engine water temperature or exhaust gas temperature, which measurement results are compared in a preprogrammed table providing the reference temperature, and wherein a measured temperature, such as the exhaust gas temperature is compared by the control unit with the reference temperature so that, when this temperature, such as the measured exhaust gas temperature, is higher than the reference temperature, the control unit has a preprogrammed temperature velocity the ignition time 35 will advance, until both temperatures are equal, while when this temperature, such as the measured exhaust gas temperature, is lower than the reference temperature, the control unit the ignition time will leave at a pre-programmed speed until both temperatures are equal, and where the correct ignition time is only determined and / or applied after the correct lambda has been found with the primary procedure. 2. Method as claimed in claim 1, which is carried out without using an oxygen sensor voltage as reference and / or without using a lambda sensor Method according to claim 1 or 2, wherein the precise composition of the poor gaseous fuel biogas supplied thereto is unknown and constantly fluctuates. 15 Method according to claim 1, 2 or 3, wherein the fuel contains an amount of methane gas (CH4) that fluctuates between 40 and 70 volume% and / or contains a proportion of CO2 gas that fluctuates between 30 and 60 volume%. 20 5. Method as claimed in any of the claims 1-4, wherein one or more of the following is applied: - the mixture temperature is measured in the inlet manifold, preferably in the joint part thereof, downstream of the optional intercooler; - the exhaust gas temperature is measured in the exhaust manifold, preferably in the joint part thereof, upstream of the possible turbocharger; - the engine water temperature is measured in the outgoing cooling water pipe, preferably immediately where it comes out of the engine block. 6. Method as claimed in any of the foregoing claims, wherein during the primary procedure the ideal lambda is found by means of a rest measurement, wherein in parallel operation the variation in the generator power is measured and in island operation the variation in the speed is measured, which variation in generator power resp. speed is a measure of engine unrest, and preferably the control regulates the gas flow through a controlled control valve in the gas supply. 5 7. Method as claimed in claim 6, wherein the lambda measurement / unrest measurement takes place in pre-programmed measurement periods and / or the control during a measurement period of the primary procedure sends the controlled control valve to the closed position at a pre-programmed speed until fluctuation in power or speed occurs after which the control sends the control valve to the open position at a pre-programmed speed until the fluctuation in power or speed has disappeared and the control considers the corresponding position of the controlled control valve as the ideal lambda value. 8. Device for carrying out the method according to any of the foregoing claims, which comprises: a control unit with an electronic ignition system, which controls the ignition voltage and the ignition time of a movable or permanently arranged Otto gas engine with gas injection or natural carburation , which control unit is adapted to read in the required parameters, to process them according to a certain protocol and then to provide the required control for the ignition system in order to create the correct engine settings over substantially the entire power range of the gas engine for optimum combustion. 30 efficiency without engine damage, wherein the control unit is arranged for applying two control procedures, a primary procedure for finding the ideal lambda, and a secondary procedure for finding the ideal combustion pressure, and from the result of both procedures the ignition system a sends; and for determining and / or applying the correct ignition time after the correct lambda has been found with the primary procedure.