Hiiii...it depends on which type of fuel you use..this link may help you

http://www.witchhunter.com/spraypattern1.php

If the fuel has various parameters such as viscosity, density, calorific value, the combustion time is different angles of injection engine efficiency is optimal

Following publication help you to decide injection angle:

http://www.sciencedirect.com/science/article/pii/S2212540X14000248

Moreover, the following publication will help you better.

J.R. Needham, M.P. May, D.M. Doyle, S.A. Faulkner,

Injection timing and rate control – a solution for low

emissions, SAE Paper 900854, 1990

First of all it is necessary to know that what type of combustion engine you are considering.  But the followings things are to be known

• The injection methodology is to be known prior to giving a precise answer. 
• As stated are you referring to the crank angle  relative to the start of injection or the fuel  injection nozzle (spray) angle?

  However, in a general a angle of fuel injection shall be varied according to the type of mixture required. 

Depended on fuel type use as well as the compression ratio of engine