Optimizing combustion in an opposed-piston, two-stroke (OP2S) diesel engine

Zusammenfassung

This study examines how Achates Power has developed the optimal combustion system for its OP2S engine through the:

● Experimental selection and identification of the best performance within the required limits for piston temperatures that are designed for modern, heavy-duty engine durability requirements

● Correlation of combustion computational fluid dynamics (CFD) to single-cylinder engine measurement results and determination of the right merit function with regard to fuel consumption, emissions and heat rejection

● Use of Genetic Algorithms (GAs) in CFD to iterate the combustion system of an OP2S engine within the available design space in order to further enhance performance

The study also provides an overview of the latest Achates Power engine performance and emissions results versus published data from the Ford Power Stroke benchmark engine. That data demonstrates best brake thermal efficiency of 48.3 percent, an increase of seven percentage points over the Ford engine. It also shows a very flat fuel map, which results in a 24 percent brake-specific fuel consumption reduction.

Finally, the study briefly highlights some of the fundamental OP2S advantages including

● Favorable surface-to-volume ratio

● Leaner combustion

● Shorter and earlier combustion

Abstract

The fundamental understanding of the ash accumulation in Diesel Particulate Filters (DPF) is a crucial requirement for designing DPFs for Heavy Duty engine applications. It is well understood, that the inorganic components of the engine lube oil are the dominating source for ash when DPFs are applied to remove soot particles from the exhaust of modern diesel engines burning diesel fuel according to DIN EN 590. A DPF of optimum size requires periodic ash removal. A typical cleaning interval between two DPF ash removal processes currently ranges between 240 kmls and 500 kmls (EURO VI, Heavy Duty, instruction manual of the OEMs). A wellestablished procedure to remove the ash particulates from the DPF inlet channels is the fluid-based backflush. Cleaning procedures using pressurized air demonstrate good results, but these techniques lack reproducibility and reliability. The stripping of the DPF with a fluid generally exhibits a better performance of the cleaned substrates. Maximum cleaning results are observed using a liquid designed to match the specific ash characteristic. Its application is the key enabler to nearly complete removal of all ash deposits in a liquid cleaning process.

The vision of lube oil without inorganic components remains. In this case, the DPF could be designed corresponding to the engine lifetime without any demand for a complex ash cleaning procedure.