1. INTRODUCTIONThe steady flow test

1. INTRODUCTION
The steady flow testing of cylinder heads is a widely
adopted procedure in the development of engines [1, 2]
and it is used to assist and assess the design of the
engine ports and the combustion chamber concerning
the engine flow capacity and the in-cylinder flow pattern
of the charge motion, which are critical to the engine
combustion performance. Although considerable efforts
have been made by research workers to explore the
most effective methodology for steady flow tests, there
are considerable diversities in the definitions of the
technical terms and techniques used in the present
experiment [1, 3], and the configurations of the flow
bench vary considerably with users.
The absence of a standard methodology has obviously
raised difficulties in the interpretation of available data
and prevented comparisons between the intake flows
characterized by different engine groups [4]. For
example, a swirl ratio of 3 quantified by one group could
mean a different value to another, and the ambiguity with
the tumble ratios is even greater. In the engine
development process, there is often a need to make
reference to bench mark designs or data published in the
literature. It is important, therefore, to understand the
original definitions of the terms and the effect of the
experimental techniques on the result. The experimental
techniques for the steady flow bench test and their
implications have been discussed by the early work of [3,
5, 6], and more recently by [1, 4, 7] but a critical
comprehensive review of the important issues is not
available.
This paper presents and discusses the important
technical issues involved in the steady flow bench test.
The purpose of the work is to provide the information
necessary for setting up or upgrading the experimental
system, either by selecting a commercially available
bench product as often practised by industry, or by
designing a flexible piping system which is usually a low
cost solution for university research groups. The critical
information is also expected to be useful to engineers
working on the development of engine cylinder heads,
particularly those involved in the steady flow tests.
Because there are so many techniques which have been
proposed and used in the practice, it is sensible to
choose only a few representative ones for review. The
Ricardo and AVL techniques are discussed here since
they are probably the most widely used in automotive
industry.
The text below is divided into six sections. Following this
introduction, the definitions of discharge and flow
coefficients are presented. The third section is devoted
to the methodology of defining the swirl and tumble
ratios, and the fourth section discusses the selection of
test conditions such as pressure drop, flow rate and also
the issues concerning blowing and suction systems.
Then, the experimental techniques for measuring the
angular flow momentum flux is reviewed in the fifth
section, and the link between the steady flow bench test
and engine combustion performance is discussed in the
sixth section. Finally, the main conclusions and
recommendations drawn from the discussion are
summarized.