4. THE SMOKELESS ENGINES
The world society's focus on different emission issues as perceived by the author's company is reflected in corresponding research (Figure 9).
4.1 No visible smoke
In the early eighties the author's company made major efforts to reduce visible smoke at low load, and systems like preheating of the charge air with waste heat, turbochargers with high efficiency at part load, and combustion space optimized for low smoke were introduced. The result was that above 25% engine load there was no visible smoke. However, at the moment it seems that that is not good enough, and the market demand is "no visible smoke at any load". In order to avoid visible smoke at any load, direct contact between fuel droplets and the combustion space surfaces must be avoided by all means. This can be done by:
・Small fuel droplets
・Short ignition delay
・High air excess
・Long distance between nozzle and piston bowl
Most of these parameters are very well optimized in today's engines, and the biggest potential lies in the fuel droplets. Fortunately the author's company started three years ago to powerfully pursue the development of common rail injection systems, both for medium-speed engines and low-speed engines. The common rail injection system offers the following features:
・Free choice of injection timing
・Injection pressure independent of engine load (Figure 10)
・Intelligent parameter relationships can be established
- Max. injection amount dependent of charge air pressure and rotational speed
- Optimized injection timing at load pick-up
・Less parasitic loads
・Smaller camshaft possible
These features can be mined into the following advantages for the customer:
・Lower fuel consumption (3 g/kWh)
・Lower NOx and possibilities to use different NOx ratings
・No visible smoke at any load
・Possible to start the engine without visible smoke
・Load cycling without smoke possible
・Lower maintenance cost
