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The Rotapac Fuel Injection Concept for Low Emissions 2-Stroke Engines
Technical Paper
93A065
Sector:
Language:
English
Abstract
For many years now IFP has been developing its patented
Compressed Air Assisted Fuel Injection system (named IAPAC) for
2-stroke engines. The idea behind the IAPAC system is to scavenge
the cylinder as much as possible with air only and to as late as
possible introduce the fuel into the cylinder in a finely atomised
form through the IAPAC poppet valve. This minimizes the quantity of
fuel short circuited and thus minimizes the level of hydrocarbon
pollutant emissions in the exhaust gas. It has already been
demonstrated that the IAPAC system is very capable of providing a
mechanically simple low cost solution in producing low emissions
and low specific fuel consumption 2-stroke engines. These IAPAC
engines have to date been developed for automotive, marine outboard
and scooter applications and are well described in many previously
published technical papers.
The purpose of this paper is to propose a new technical solution
that increases the potential of the IAPAC concept and its field of
application. This new technical solution, named ROTAPAC, is based
on the use of a rotary valve, instead of a poppet valve, as the
means of introducing the fuel air mixture into the cylinder. As for
the poppet valved IAPAC solution, the rotary valve must atomise the
fuel to provide a finely atomised fuel air mixture in the
cylinder.
It is expected that this new concept will give more flexibility
in the engine design such as a more compact cylinder head. However
one of the main points of interest in this new technical solution
is the possibility to extend the range of application of the IAPAC
process to more high speed engines, such as high performance
motorcycle engines. This extension to the range of application is
mainly due to the higher maximum valve train RPM limit that can be
achieved with a rotary valve system. Nevertheless these expected
advantages and the validity of the concept must firstly be
demonstrated, as was the purpose of this study.
At first it may seem that, since the IAPAC system is only used
to introduce a relatively cold air-fuel mixture, it may be
relatively easy to design a rotary valve system that would fulfill
the requirements of the compressed air assisted fuel injection
process. In fact, the work presented in this paper will show that
the implementation of such a device, that works correctly, presents
several technical problems which have to be overcome. Some of these
technical problems are already well known, as for example the
traditional combustion chamber sealing and lubrication
difficulties, but in addition other unexpected problems were also
encountered.
This paper describes the ROTAPAC design concept and the
solutions proposed to solve all the technical problems
encountered.
Some preliminary results from a 125 cc 2-stroke motorcycle
engine converted to ROTAPAC are finally presented and the benefits
of such a concept are discussed.
The conclusion at this stage of the development work is that the
ROTAPAC fuel injection concept represents an attractive solution
which seems realistic and viable for its introduction as an
alternative to the poppet valved IAPAC system in the production of
low emissions 2-stroke engines.
The successful use of the IFP compressed air assisted fuel
injection process, named IAPAC, has been previously well
demonstrated on 2-stroke outboard marine engines [1,2] and
motorcycle engines [3,4]. The IAPAC injection process allows
significant reductions in pollutant emissions levels and brake
specific fuel consumption to be obtained without losing the
inherent principle advantages of the pump crankcase scavenged
2-stroke engine [5].
IFP has shown in the above referenced publications, that it is
possible to convert a conventional "thirsty" and
"polluting" 2-stroke engine, to one of low pollutant
emissions levels with low brake specific fuel consumption, by the
implementation of the IAPAC process alone. The complete engine
conversion can be achieved with relative simplicity and, very
importantly, with low additional production cost [4]. Further
reductions in pollutant emissions levels and brake specific fuel
consumption, especially at low speed low load, can be obtained by
the additional use of, for example, an exhaust throttle [6, 7] or
transfer throttle [8, 9], to more precisely control the internal
fluid dynamic processes. Also, further reductions in pollutant
emissions levels over the entire speed and load range can be
obtained by the implementation of a small oxidation catalyst [1,
10], which, due to the low levels of hydrocarbon emissions in g/hr
at high engine speeds and loads, is compatible with an IAPAC
converted engine.
For 2-stroke outboard or motorcycle engines, it is important to
conserve certain inherent 2-stroke engine qualities if the
implementation of any fuel injection process, aimed at being
competitive in the pursuit of reductions in pollutant emissions and
fuel consumption, is to be successful. These inherent qualities are
the packaging, light weight, high specific power, mechanical
simplicity, low frictional and pumping losses and very importantly,
the lost cost. To this end IFP has developed and simplified its
IAPAC injection process for motorcycle [3, 4] and outboard marine
[1, 2, 10] applications and, for the same reason, is at the moment
developing the concept of replacing the IAPAC poppet valve by a
rotary valve. It is expected that the eventual introduction of this
alternative concept will, while retaining the other IAPAC
advantages [1-10], help to reduce the cost and simplify the
mechanical design, with a positive impact in terms of engine height
and weight, to give lower frictional losses and therefore slightly
further improved efficiency, and at the same time to increase the
RPM and high specific power limits which could be imposed by the
valve train in some particular applications.
The purpose of this paper is to present the preliminary results
of a research program to develop a rotary valve that could
successfully represent an alternative to the use of poppet valves
in the IAPAC circuit for some particular applications.