Diesel engines are getting close to the theoretical limits of efficiency. To show how far we have come, consider Rudolf Diesel. On Feb. 17, 1897, he demonstrated an efficiency of 26.2% with the engine he made. In contrast, the average steam engine he was competing with was around 10% efficiency. Fuel systems are an area that have had major improvements in both the components themselves, like injectors and fuel pumps, and on the control side with faster engine control modules and better software. There are too many systems used over the years to go into detail on all of them, but they include:
- Air blast—fuel is blown into the cylinder by a blast of air.
- Solid fuel/hydraulic injection— fuel is pushed through a spring loaded valve/injector to produce a combustible mist.
- Mechanical unit injector—injector is directly operated by a cam, and the fuel quantity is controlled by a rack or lever.
- Mechanical electronic unit injector is operated by a cam, and the fuel quantity is controlled electronically.
- Common rail mechanical injection— fuel is at high pressure in a common rail and controlled by mechanical means.
- Common rail electronic injection—fuel is at high pressure in a common rail and controlled electronically.
Many modern-day manufacturers are moving toward the use of common rail fuel systems like the system illustrated in the above graphic. In this system, fuel is shared between injectors in a “common rail” sometimes integrated inside the cylinder head. Some of the advantages of these systems are:
- On demand fuel pressure;
- Higher injection pressure and finer atomization; and
- Possibility to have multiple injections per combustion.
And the benefits include:
- Reduction of overall exhaust emissions;
- Reduction of particulate emissions;
- Less noise; and
- Improved fuel efficiency.
This article was contributed by Kurtis Schneider, technical editor for Mitchell 1’s Commercial Vehicle Group.
