**Section 3**

**Numerical Studies on Injection Process Phenomena** 

84 Fuel Injection in Automotive Engineering

Patterson, M.A.; Kong, S.C.; Hampson, G.J. & Reitz, R.D. (1994). Modeling the Effects of Fuel

Patterson, M.A. (1997). *Modeling the Effects of Fuel Injection Characteristics on Diesel Combustion* 

Rychter, T. & Teodorczyk, A. (1990). *Mathematical Modeling of Piston Engine Working Cycle* (in

Shaded, S.M.; Chiu, W.S. & Yumlu, V.S. (1973). A Preliminary Model for the Formation of

Studies. SAE Technical Paper 730083, *SAE Trans,* SAE Inc., Warrendale, PA Wajand, J.A. (1988). *Compression ignition engines* (in Polish: Silniki o zapłonie samoczynnym),

Woś, P. (2008). *Effect of Fuel Injection Rate on Combustion and NOX Emission in Diesel Engine.* 

Zabłocki, M. (1976). Fuel Injection and Combustion in Diesel Engines (in Polish: Wtrysk i spalanie paliwa w silnikach wysokoprężnych). WKŁ, Warsaw, Poland

cyfrowa). Report No.3.41.1.6, Institute of Aviation, Warsaw, Poland Orzechowski, Z. & Prywer, J. (1991). *Spraying liquids* (in Polish: Rozpylanie cieczy). WNT,

ISBN 83-204-1378-8, Warsaw, Poland

ISBN 978-830-1096-42-7, Warsaw 1990,.

WNT, ISBN 978-832-0401-68-4, Warsaw, Poland

ISBN 978-83-7199-519-4, Rzeszów, Poland

Paper 940523, *SAE Trans,* SAE Inc., Warrendale, PA

*and Emissions*. Ph.D. Thesis, University of Wisconsin-Madison

bezpośrednim na podstawie charakterystyki wtrysku - część II: Symulacja

Injection Characteristics on Diesel Engine Soot and NOX Emissions. SAE Technical

Polish: Modelowanie matematyczne roboczego cyklu silnika tłokowego). PWN,

Nitric Oxide in Direct Injection Diesel Engines and Its Application in Parametric

*Mathematical approach* (in Polish: Wpływ przebiegu wtrysku paliwa w silniku wysokoprężnym na spalanie i emisję NOX). Rzeszów University of Technology,

**5** 

 *USA* 

**Influence of Nozzle Orifice Geometry** 

**Characteristics of a Diesel Injector** 

Sibendu Som1, Douglas E. Longman1, Anita I. Ramirez2 and Suresh Aggarwal2

> *1Argonne National Laboratory, 2University of Illinois at Chicago,*

**and Fuel Properties on Flow and Cavitation** 

Cavitation refers to the formation of bubbles in a liquid flow leading to a two-phase mixture of liquid and vapor/gas, when the local pressure drops below the vapor pressure of the fluid. Fundamentally, the liquid to vapor transition can occur by heating the fluid at a constant pressure, known as boiling, or by decreasing the pressure at a constant temperature, which is known as cavitation. Since vapor density is at least two orders of magnitude smaller than that of liquid, the phase transition is assumed to be an isothermal process. Modern diesel engines are designed to operate at elevated injection pressures corresponding to high injection velocities. The rapid acceleration of fluid in spray nozzles often leads to flow separation and pockets of low static pressure, prompting cavitation. Therefore, in a diesel injector nozzle, high pressure gradients and shear stresses can lead to

Cavitation, in diesel fuel injectors can be beneficial to the development of the fuel spray, since the primary break-up and subsequent atomization of the liquid fuel jet can be enhanced. Primary breakup is believed to occur in the region very close to the nozzle tip as a result of turbulence, aerodynamics, and inherent instability caused by the cavitation patterns inside the injector nozzle orifices. In addition, cavitation increases the liquid velocity at the nozzle exit due to the reduced exit area available for the liquid. Cavitation patterns extend from their starting point around the nozzle orifice inlet to the exit where they influence the formation of the emerging spray. The improved spray development is believed to lead to more complete combustion process, lower fuel consumption, and reduced exhaust gas and particulate emissions. However, cavitation can decrease the flow efficiency (discharge coefficient) due to its affect on the exiting jet. Also, imploding cavitation bubbles inside the orifice can cause material erosion thus decreasing the life and performance of the injector. Clearly an optimum amount of cavitation is desirable and it is important to understand the sources and amount of

The flow inside the injector is controlled by dynamic factors (injection pressure, needle lift, etc.) and geometrical factors (orifice conicity, hydrogrinding, etc.). The effects of dynamic

**1. Introduction** 

cavitation, or the formation of bubbles.

cavitation for more efficient nozzle designs.
