Numerical investigation of scaling effects for heavy-duty ammonia/diesel dual fuel engines

Abstract

Numerical scaled-model investigations based on similarity theory provide an effective way to accelerate engine development while reducing costs and time. However, their application in ammonia/diesel dual fuel engines is still rarely reported. This study establishes and numerically validates for the first time a scaling method for the low-pressure dual fuel (LPDF) mode of heavy-duty ammonia/diesel engines based on the speed law of similarity theory. Five geometrically similar engines were simulated with scaling factors ranging from 0.8 to 2.08, and the models were rigorously validated based on experimental data. The results show that under the speed law, spray penetration and shape, cylinder pressure, heat release rate (HRR), ignition timing, flame propagation, and combustion phase show excellent similarity across all scales, while emissions exhibit good overall similarity with minor quantitative deviations attributable to the temperature-sensitive nature of pollutant formation. Due to the larger surface to volume ratio (S/V) of smaller engines, heat transfer losses increase, but the exponential function accurately correlates this loss with the scaling factor. This work proves for the first time that the scaling method based on the speed law can effectively retain the spray, combustion, emission and heat transfer characteristics of the engine size as long as the geometric similarity and single value conditions are met. These findings provide a theoretical basis for accelerating the development of ammonia engines using existing platforms, which may significantly shorten the development cycle and reduce costs.