Browse Publications Technical Papers 2007-01-0911

Optimization Towards Low-temperature Combustion in a HSDI Diesel Engine, Using Consecutive Screenings 2007-01-0911

This paper describes the optimization process of a small single-cylinder research HSDI diesel engine, starting from a conventional combustion towards split-injection low-temperature combustion.
Targets for emissions, fuel consumption and combustion noise are defined with the characteristics of low temperature combustion in mind, in other words, high CO, HC and combustion noise but low soot and NOX.
In this investigation the targets are defined for a medium-load working modes of a typical small four-cylinder turbo-charged diesel engine, equipped with a particulate trap and oxidation catalyst. They are introduced into an objective target function which is a guide for the optimization process.
The statistical optimization procedure used is the method of consecutive screenings. With this methodology, six factors are optimized: mass distribution of the fuel injection pattern, injection pressure, combustion phasing, EGR rate, boost pressure and dwell time between injection events.
For each consecutive screening round, a response surface of the objective target function is built which is optimized with a steepest ascent method. The optimum serves to define the next screening round. The final optimum settings are characterized by a late split-injection and a high EGR rate. The two injection events lead to two auto-ignition delay events, resulting in a highly premixed combustion. This combustion mode is characterized by very low levels of nitrogen oxides (10∼15 ppm) and low combustion noise at reasonable fuel consumption, soot, HC, and CO emission.


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