Prins VSI CNG, Installation Manual

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Copyright © Prins Autogassystemen B.V. 2013 Page 5
Introduction
VSI stands for “
vapour sequential injection
”, it points directly to the most important properties of the system.
This second-generation gas injection system is based on a vapour LPG/CNG injection that is injected
sequentially in the engine. Sequential means that the gas injectors will inject the LPG/CNG in the sequence
equal to the injection sequence of the petrol injectors,
This sequence in most applications is equal to the firing order of the ignition sequence of the engine, for
example with a 4-cylinder engine this is normally 1-3-4-2. Sequential injection means that the amount of
injected fuel per cylinder the can be metered and timed individually.
This achieves a much higher level of performance emission and drivability. The VSI system was designed
and developed in-house by Prins Autogassystemen B.V.
VSI characterizes itself with a high level of integration into to the petrol management system. The two
systems integrate as “master-slave” system.
This means that the original petrol management ECM controls the amount of LPG/CNG injected via the gas
injectors into the engine. The VSI ECM only translates the relevant signals coming from the engine
management system necessary for MASTER /SLAVE strategy.
Following this strategy the petrol management system is the “MASTER” and the VSI ECM the “SLAVE”.
The advantage of this strategy: while driving on LPG/CNG the lambda control and OBD functions keep
within the OE parameters, functioning correctly and controlled by the petrol management system. So when
operating on LPG/CNG it is not necessary to generate simulated signals.
There is one exception made for the petrol injector signals, while driving on LPG/CNG the petrol injector’s
are switched off to discontinue the petrol supply. To maintain the injection control signals it is necessary to
simulate the petrol injectors to ensure the original ECM does not detect a fault code. Secondly when
operating on LPG/CNG it is necessary to maintain a petrol injector control signal to measure the required
fuel demand.
The second generation injection system VSI has the ability to inject sequentially making it quicker and more
accurate, large benefits can be gained in engine and emission performance.