Flow bench testing of prototype intake manifolds for ultralight aircraft engine

The article describes the research on the intake manifold for ultralight aircraft engine Vaxell 100i. It presents the actual and new redesigned manifold construction and points out the design requirements. The results of previously made numerical simulation of air flow inside the manifold are discussed. Computer analysis confirmed the appropriateness of internal guide vanes usage to improve the uniform air distribution between cylinders. For verification, a flow bench test stand was made for multicylinder intake manifold testing. A prototype manifold was built with the possibility of guide vane adjustment. The best variant had almost 5 times better uniformity of air distribution comparing to variant without the guide vane. Flow bench results confirmed the conclusions from numerical simulations.


Introduction
The intake system aim is to transport a proper amount of air or air-fuel mixture to the combustion chamber to ensure engine achieves the assumed parameters -power and torque curve, fuel consumption and emission.An intake manifold is located between throttle or carburettor (which is often still used in engines for aircraft propulsion) and head intake ports, and it consists of the main inlet, "plenum" (central air volume) and "runners" (individual tubes leading to cylinder head ports).The construction of intake manifold has to meet specific requirements, of which the most important are [1,2]: • low air flow resistance, • even distribution of air flow between each cylinder intake ports [3], • runner geometry (length, cross-section shape and dimensions) ensuring the usage of pulsating air wave effect that occur in the intake system, • tailpipe emission [4,5].
In the case of manifolds for ultralight aircraft engines, additional assumptions must be met: • low weight while retaining sufficient strength and stiffness, • adequate air flow around the head and cylinders for cooling (manifold construction cannot limit it), • the low overall height of the intake system (maintaining compact size relative to the external dimensions of the engine and its accessories).Complying with the above requirements makes the ultralight aircraft intake manifold design process complicated and the final design is a result of technical compromises.For these reasons, we performed a numerical flow simulations, followed by a flow bench testing of prototype manifold.

Research object description
The object of the research was an intake manifold used in Vaxell 100i engine, which drives many transportation vehicles including ultralight and light aircrafts (Tab. 1, Fig. 1).The disadvantages of actual intake system design are large numbers of parts and large dimensions.That plays a significant role in the application for ultralight engines, hence a decision of intake system modification.A 3D model (Fig. 2) of changed manifold was designed with one big throttle on the main inlet, smaller plenum and straight runners -in the further part of the article marked as manifold 1.Additionally, variants with guide vanes were designed.This model has been analyzed using Ansys-AIM numerical simulation software [6].
Flow bench testing was performed on newly designed inlet manifold (Fig. 3) with a prototype air tank (Fig. 4) -marked as manifold 2 in the rest of the paper.The special air tank consists of an aluminum cast (1) with a planned upper surface and welded flange.From the top, the p (2) mounted printed guide The position by 12 mm.A with 3 diffe cover is tra carrying out inside the ta works.

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Conclusions
Research have shown the correctness of design and construction of a special intake manifold flow test bench.It enables to measure the mass airflow in each of the manifold outlets and analyze its distribution for multicylinder engines.The flow bench test results confirmed the numerical simulation conclusion, that application of a guide vane inside the intake manifold improves the uniform distribution of the airflow between the cylinders.For the manifold without vane the maldistribution coefficient D g = 0.44 was obtained while using guide vane in the best configuration (-6 mm, +12.5°) the factor D g = 0.09 was obtained.In the worst configuration (0 mm, -12.5°)D g was 0.60.In this case, the guide vane distributed the majority of airflow to outlet number 1 and 2, so that other outlet received less air flow.
Performed tests do not take into account the wave pulsation effects which occur in the engine intake system.In order to check its influence in the prototype manifold, engine tests on the dynamometer are planned in the future.
Guide vane is an additional element in the intake manifold and it has an impact on airflow resistance.That is why a study on guide vane influence on air flow parameters is planned.

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