Flow Characteristics of a Gas-Blast Fuel Injector for Direct-Injection Compression-Ignition Engines

Abstract

Natural gas has a high auto-ignition temperature, therefore natural gas engines use an ignition source to promote combustion. The high-pressure direction-injection (HPDI) systems available use small diesel injections prior to the main gas injection. A new series of HPDI injectors have been developed that inject diesel and gas simultaneously through the same holes. In order to understand and control injection and combustion behavior in an engine, it is essential to understand how injection mass is related to the diesel/gas ratio and injection command parameters. Three prototype injectors are examined. "Prototype B" most closely resembles a standard J36 HPDI injector, but has a modified diesel needle that injects diesel internally into a common diesel/gas reservoir. Prototypes "CS & CSX" have the diesel needle eliminated and replaced with a flow restrictor. The pressure difference between the diesel and the gas controls the quantity of diesel injected. A single pulse width (GPW) for the gas needle controls the fuel quantities. An injection visualization chamber (IVC) was developed for flow measurements and optical characterization of injections into a chamber at pressures up to 80 bar. Diesel and natural gas are replaced by VISCOR® and nitrogen to study non-reacting flows. A novel feature of the IVC is a retracting shroud that allows the injector to reach steady-state prior to imaging. For low commanded injection duration (GPW less than 0.60 ms), the relation between GPW and injected mass is non-linear, for all injectors tested. For gas pulse widths greater than 0.65 ms the Co-injectors exhibit approximately linear behavior with higher diesel fuelling quantities lowering gas flow quantities. All Co-injectors are compared to baseline gas flow quantities of a standard J36 to show design difference effects on flow quantities. The sensitivity of gas flow to diesel in injection quantities, as well as the discharge coefficient are computed and theoretically modeled for each prototype. Results suggest differing diesel/gas distributions, dependent on method of diesel introduction and actuator response. Chapter 1-Introduction 1 1.1 Limitations of Diesel Engines 1 1.2 Diesel Engine Emissions 3 1.3 Natural Gas Compression-Ignition 6 1.4 Objective and Scope 9 1.5 Thesis Structure 10 Chapter 2-Background and Motivation 11 2.1 Dual-Fuel Compression Ignition Engines 11 2.2 High-Pressure Direct Injection of Natural Gas 12 2.3 Co-Injection of Diesel/Natural Gas 15 2.3.lPriorWork 15 2.3.2 Current Work 17 2.3.3 Early Flow Characterization 2.4 Spray Visualization Chapter 3-Apparatus and Procedures 3.1 Injectors 3.1.1 J36 and Co-injector B 3.1.2 Co-injector CSX and CS 3.1.3 Injector Command Parameters 3.2 Injector Visualization Chamber (IVC) 111 3.3 Spray Extraction Shroud 38 3.4 High-Speed Camera 40 3.5 Gas and Liquid Supply and Measurement 3.6 Control System, Data Acquisition, and Triggering 43 Chapter 4-Results and Discussion 45 4.1 Experimental Design 46 4.1.1 Flow Characterization 46 4.1.2 Chamber Pressure Effects on Co-injector F...

Compression ignition of directly injected natural gas with entrained diesel

“…The variations shown in Table 3 are consistent with flow experiments and injector dynamics modelling [19]. Higher chamber pressures delay the needle closing, so that for a specified injection mass the commanded GPW is smaller.…”

“…During the first gas injection, the mixture of diesel and gas is injected into the combustion chamber. Based on spray visualization [19] and the low liquid/gas ratio of this two-phase injection process, it is believed that the diesel is very finely atomized. After the pilot injection, the gas needle lifts again and the main charge of natural gas is injected, carrying with it some diesel remaining in the plenum after the first injection.…”

“…The total ignition delay consists of the electromechanical delay, the physical delay, and the chemical delay. The electromechanical delay is the interval between the injection command signal and the needle opening; it has been found to be , 0.9 ms for the co-injector, relatively independent of cylinder pressure [19]. In subsequent figures showing ignition delay, the electromechanical delay has been removed to more accurately show the physical and chemical delay.…”

Comparison of injectors for compression ignition of natural gas with entrained diesel

“…The total ignition delay consists of the electromechanical delay, the physical delay, and the chemical delay. The electromechanical delay is the interval between the injection command signal and the needle opening; it has been found to be , 0.88 ms for the co-injectors, relatively independent of cylinder pressure [14]. In subsequent figures showing ignition delay, the electromechanical delay has been removed to more accurately show the physical and chemical delay.…”