Optical study of Tumble, Spray and Combustion

Abstract

The automobiles of today are getting more fuel efficient in order to meet future emission standards. It is also important to have more fuel efficient engines than the competitors. The consequence is that engine development is intensified and more ideas needs to be tested thoroughly. One of the ideas at Volvo cars is a tumble flap. The tumble flap is controlled to close a predefined part of the intake port in order to increase the tumble motion in the combustion chamber. A tumble motion is a circular motion with it's axis of rotation parallel to the engine head. To make the effects of the tumble flap clearly visible an optical engine is used. An optical engine has a cylinder and piston made of glass which makes it possible to record what happens in the combustion chamber while the engine is running. The fuel is injected directly to the combustion chamber, so called direct injection engine. This gives excellent opportunity to see how the spray is affected by an increased tumble motion. The effect on the combustion could be seen when changing parameters. The events appear in a fraction of a second why a high speed camera is used to capture the events. It has been shown that the spray is mostly effected in a late phase of the intake stroke. The spray is stable and relatively small in the early stage and is therefore only mildly effected by the ongoing gas motion. With the tumble flap activated, it is possible to observe that fuel is moving back to the valves before it is evaporated. Sometimes it is possible to see a tumble motion within the spray. If the injection pressure is increased, the initial spray stability will increase, the fuel reaches further before it is effected of the ongoing gas motion. The combustion takes place considerably faster with the tumble flap restriction. A problem with the tumble flap is that diffusion flame combustion may occur due to an increased risk of wall wetting.

Popular Abstract

Optical Study of tumble, Spray and Combustion
This is an optical study of a tumble inducing system for a direct injected gasoline engine. The tumble flap is a system that blocks part of the intake. It has the purpose to promote mixing of fuel and give more stable and faster combustion. These wanted behaviours could be seen in the study.
The Master´s thesis was a study of the gas movement inside a direct injected gasoline engine. The study was made with an optical engine. The aim of the study was to evaluate a so called tumble flap system and how the system interacts with the injected fuel and affects the combustion. The engine had a glass piston and a cylinder wall made of glass. The combustion and also the fuel spray was studied by filming the combustion chamber through the glass. Variations of certain parameters such as tumble flap position, engine speed and fuel pressure were made to investigate the system in an effort to understand how the tumble flap system works for different conditions. Some really interesting results were seen in the investigation, such as more rapid combustion which is better for the engine efficiency due to less time for heat transfer to between the combustion chamber and walls, but also results that indicates the need for more investigation to understand the system completely. From the spray study some very interesting results were collected. The spray was affected in such a way that the stronger so called tumble motion could be observed clearly. The study was made at Volvo Cars Corporation with
their optical engine.
The system as such has the possibility to improve fuel consumption and emissions of a petrol engine.
It is important to understand the fuel/air interaction when designing the combustion system. The current trouble with this type of engine is that the fuel consumption too high to meet coming laws in emissions in terms of for example CO2 and soot. CO2 have negative effect on climate and soot is a health issue. For this reason it is important to decrease the fuel consumption of the DISI engines and as mentioned before the purpose of a tumble flap system is to achieve lower fuel consumption.
The knowledge learned and the observed behaviours can be very useful when the tumble flap system is tried on a full metal engine or so called real engine. This is due to observed behaviours in the optical engine that can explain what happens in the full metal engine. It can also be used as input for the development of the engines. It can be important to be able to see the connection between what happens in the metal engine to what was seen in the optical engine study. The causes of problems can be directly seen in the optical engine. In a metal engine you only have the results of what happened and can not see the direct link between the problem and cause. The study can also be used to understand calculations and simulations for the tested system. It can also give possible input to the simulations.
One very interesting observed with the tumble flap system was the possibility of moving the ignition closer to top dead center due to the faster combustion. It will give the possibility to take out more power in the expansion stroke.

• author: Eriksson, Martin and Ryrholm, Robin
• supervisor: Martin Tunér
• organization: Department of Energy Sciences
• course: MVK920 20151
• year: 2015
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Tumble ap, Direct Injection Spark Ignition, Keywords: Optical engine
• report number: LUTMDN/TMHP-15/5335-SE
• ISSN: 0282-1990
• language: English
• id: 7356939
• date added to LUP: 2015-06-16 14:39:50
• date last changed: 2015-06-18 14:04:27