Re: Direct Fuel Injection

Greetings:

Direct fuel injection has been used on diesel engines for most of the 20th 
century while their adaptation to other types of mass produced internal 
combustion engines have occurred during the latter half of the century.  In 
a modern automotive diesel engine the fuel injection pump on each cylinder 
must supply fuel at a pressure of between 350 and 1200 bar (one bar = 0.987 
standard atmosphere) to be injected into a cylinder during the peak of the 
compression cycle. The start of the injection cycle must be precisely timed 
to within one degree of crankshaft rotation to achieve the optimum 
compromise between fuel consumption, emissions and combustion smoothness 
(noise). These parameters have made direct injection by strictly mechanical 
means (gears, shafts and belts) a difficult and expensive technique and a 
continued maintenance problem. More recently the development of 
electronically controlled direct injection pumps have led to their being 
used in mass manufactured vehicles. Two brief history charts for diesel 
engines and injection systems can be found at the following URLs:
 
http://www.lucas.co.uk/lds/history/history.htm
This page offers an insight into the century of innovation leading to
today's diesel engines and also a brief tabular history of Diesel...
http://www.psa.fr/en_psaBB0026.html

The need for improved engine performance with reduced exhaust emissions has 
led to many improvements in engine management systems. From the widely used 
single carburetor systems to multiple carburetors,  to single-point fuel-
injection and to multiple point fuel injection has been a continuing  
evolutionary process to obtain optimum engine performance with high fuel 
efficiency and minimum emissions. 

Multiple carburetor systems were an early technique used to greatly 
increase engine power; however, this became an expensive, inefficient, 
bulky technique for precisely metering fuel into the intake manifolds of 
internal combustion engines.  Single point (central, or in-line) fuel 
injection systems inject fuel into the intake manifold above the throttle 
at a pressure of about one bar above atmospheric pressure.. This enables a 
precise control of fuel flow using an inexpensive electric fuel pump 
similar to that used with carburetors but with much improved electronic 
control of fuel distribution. The Bosch "Mono-Jetronic" is an example of 
this type of low pressure fuel injection system.

Multiple point fuel injection with injectors placed nearer the cylinders is 
a low pressure improvement over the single point system. The Bosch "KE-
Jetronic" represents this type of fuel metering system with increased 
control.

Finally the direct injection of fuel at high pressure into each cylinder 
gives the maximum control of engine performance with the elimination of 
bulky intake manifolds and their assorted fixtures. These systems require 
precise sensors and control by an electronic computer which in turn leads 
to large improvements in engine performance which is also programmable for 
the particular application. 

Today the operating tables in engine management computer ROM memory  are 
average parameters determined by measurements made from thousands of 
production engines.  In the future each cylinder will have individual 
pressure and flow sensors for closed loop, real time control to optimize 
the operation of each cylinder in the engine. For example our laboratory 
has developed a miniature, low cost, fiberoptic pressure sensor that mounts 
within the ceramic body of a spark plug, to accurately measure pressure 
cycles in each cylinder of an engine for fuel and ignition control. Optical 
fibers are very small and are immune to the large electrical noise produced 
by the spark plug electrical arcs that plague most electrical sensors. We 
expect this type of closed loop control for each cylinder's performance to 
eventually provide significant improvements in power, efficiency and 
reduced emissions in future automotive engines.

Best regards, your Mad Scientist

Adrian Popa