2 General
KRONOS 20
7
necessary. This results in a greater influence of the main adjusting screw which is able to
regulate the air-fuel-ratio within a limited range.
Theoretically it is possible fit gas bores on a Venturi tube in a way to cover the whole calo-
rific value range for an application, e.g. from propane to landfill gas, as long as there is a
possibility to compensate the differences relating to calorific value, air-fuel-ratio and gas
density with the volume flow control.
This means that a MAS with a definite relation between valve position and opening cross-
section may be placed in a way to obtain a desired air-fuel-ratio. But usually mixers for a
specific gas quality are designed to give the gas control valve only limited adjusting au-
thority.
A digitally controlled MAS like the HEINZMANN E-LES (digital lambda adjustment
screw) that receives its inputs from a speed and load dependent map and reacts to gas pres-
sure and mixture temperature variations, makes it possible to obtain an ideal gas-air mix-
ture under all operating conditions.
Based on measured signals such as engine speed, inlet manifold pressure, mixture tempera-
ture as well as on programmed parameters such as engine displacement and volumetric ef-
ficiency the mixture flow may be calculated. The stored gas data and the mixer and gas
valve characteristics allow to calculate current pressure conditions and gas flow. This al-
lows a mixture control according to the physical model of a Venturi based system.
The valve cross-sectional area calculated by the control unit and the according valve posi-
tion are adjusted accordingly by a stepping motor.
For engines of the same type no different parameter settings are required. In case of differ-
ent gas quality only the gas bores must be adapted.
2.6
General Application
The gas valve E-LES may be used for the following applications:
•
As conventional MAS
In this application, the parameters relating to the desired valve position / gas valve
cross-sectional opening area are set to the desired parameter value. Different settings
may be implemented and reproduced simply by changing the parameter. Non mechani-
cal adjustments are required. This mode of operation can be convenient when gas type
changes frequently. The right to effect changes may be limited by assigning specific
permissions. The settings may be changed via a remote connection.
•
As Positioner
The desired valve position / gas valve cross-sectional opening area are adjusted by the
control unit according to a set value derived from an external control (current / voltage
signal). This allows to include the system in an external lambda regulating system.
•
As stand-alone Gas Mixture Control System
Summary of Contents for E-LES 30
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