Access Type

Open Access Dissertation

Date of Award

January 2011

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Mechanical Engineering

First Advisor

Naeim A. Henein

Abstract

ABSTRACT

OPPOSING EFFECTS OF RECIRCULATED GASES DURING CRANKING ON COLD START OF DIESEL ENGINES

by

RAFIK ROFAIL

August 2011

Advisor: Dr. Naeim Henein

Major: Mechanical Engineering

Degree: Doctor of Philosophy

Enhancing cold start of DI diesel engines is the motivation behind this study. A new control strategy is proposed to reduce the cranking period and the white smoke emissions. In the strategy, the gases leaving the cylinder during the cranking period are recycled back into the intake manifold using two different methods. In the first method the engine-out gases during cranking are recirculated into the intake manifold and their rate is controlled by a CGR (Cranking Gases Recirculation) valve, without applying any back pressure on the engine. In the second method a butterfly valve is installed in the exhaust system after the turbocharger to increase the back pressure and the rate of recirculated gases. Since there is no combustion during cranking, these gases contain evaporated hydrocarbons (HCs) and partial oxidation products such as formaldehyde (HCHO). HCs and HCHO have two opposing effects. HCs enhance the autoignition process, while the HCHO has an opposite effect. These opposing effects are being investigated by three different approaches. The first is experimentally in a multi-cylinder proto-type engine. The second is using high speed imaging in an optically accessible engine. The third is by using CFD and chemical kinetic simulation to gain a better understanding of the effect of the recirculated gases on the autoignition process during cold starting of a direct injection diesel engine. Cold start experiments are conducted on a 1.2L Ford DIATA 4-cylinder, 16-valve, 70 mm bore, 78 mm stroke and 19.5 compression ratio, water cooled, turbocharged and intercooled diesel engine. The engine is equipped with a common rail injection system, EGR system and a swirl control mechanism. The engine is installed in a cold room and the ambient temperature is electronically controlled. Before starting, the engine is soaked at the desired room temperature for at least eight hours. The analysis of the data demonstrated the effect of two CGR methods on reducing the cranking period and HCs emissions. The images showed the effect of aldehydes on hindering the autoignition and combustion processes. The simulation covered a wide range of the hydrocarbons and aldehydes concentrations and their effect on the ignition delay. The simulation results agreed with the experimental findings. The results of this work will help in developing strategies to reduce the cranking period, fuel consumption and white smoke emitted during cold starting of diesel engines. In addition, a more understanding will be developed of the role of aldehydes in combustion instability and misfiring after first firing experienced in cold starting of diesel engines.

Download

Share

COinS