var game = new Phaser.Game(800, 600, Phaser.AUTO, 'phaser-example', { preload: preload, create: create });

function preload() {

    game.load.image('alien', 'assets/sprites/space-baddie.png');

}

function create() {

    var emitter = game.add.emitter(game.world.centerX, game.world.centerY, 250);

    emitter.makeParticles('alien');

    emitter.minParticleSpeed.setTo(-300, -300);
    emitter.maxParticleSpeed.setTo(300, 300);

    //  By setting the min and max rotation to zero, you disable rotation on the particles fully
    emitter.minRotation = 0;
    emitter.maxRotation = 0;

    emitter.start(false, 4000, 15);

}