Unit pump

Introduction

The Diesel engine has been under a lot of changes lately, many of them being related to the unique fuel control process that distinguishes the diesel engine from the petrol alternative. While the petrol engine has to contend with a separate ignition system to operate, it is the fuel system itself in the diesel engine that acts as an ignition system. Recent new technologies in petrol engines have introduced changes in the way the fuel ignites by modifying the ignition cycle to great complexities, resulting in technologies such as Honda's Intelligent Dual Spark plug Ignition (i-Dsi)

Diesel engines too have benefited from the addition of systems such as Common Rail Injection

Most of these new fuel management systems are created for the following objectives-

1. Increasing fuel injection pressures to the ranges of 1000-1200 bar, which result in better fuel atomisation.

2. Enabling the use of electronic actuators at the apex of the fuel delivery system, to gain precise control over the timing, quantity and interval of multiple injections with an ECM

Both these objectives are intended to make the diesel engine more fuel-efficient, powerful and ecologically-friendly.

Similarities between Common Rail and Pumpe Düse systems--

Both the systems take advantage of Electronic fuel injection actuators, which are again predominantly of 2 types--

1. Solenoid control actuators

2. Piezoelectric crystal actuators

Another shared feature is the Electronic control module or ECM and the use of electric pumps as the primary fuel delivery system.

Workings of the Pumpe Düse system

The Crankshaft of the engine drives a pump camshaft, with an equal number of cams as the number of pistons, which is located to one side of the engine as opposed to the top, that is the case in OHC engines. Each cam drives a Unit Injector, the heart of the system. The Unit Injector works on the principle of Hydraulics, using a small mechanical pump to pressurise fuel to very high levels.

The Unit Injector is basically a piston driven by the cam below in a small cylinder. There is a fuel inlet port that opens as the piston slides down, delivering fuel under pressure into the cylinder, from an electric pump. As the cam turns, the port closes and the fuel is pressurised further, ready to be released by the electronic actuator that opens and closes by command of the ECM. The actuator thus is able to deliver fuel from the Unit Injector into the combustion chamber at very high injection pressures of 1600-1800 bar, in various injection modes and programs.

Of course, the entire array of Unit Injectors is usually miniaturized and built into a single-piece instrument when in practical use.

Although the Common Rail injection approach is said to build quieter, smoother engines, the Pumpe Düse system offers more torque, and less pollution. The problems of excess mechanical and combustion noise and vibration have been filtered out by refinements to the system.