Experimental and Numerical Analysis of a Dual Fuel Operation of Turbocharged Engine at Mid-High Load

In the paper the operation of a turbocharged dual fuel engine at mid-high load is investigated on a single cylinder experimental engine complemented by a full 0D/1D simulation model that provides boundary conditions for the experiment and full engine system results. When duel fuel combustion mode is used on a turbocharged engine with the variable geometry turbocharger, the mid-high load operating points can be obtained with number of different combinations of intake pressure and excess air ratio. Besides the impact on combustion, the specific combination of intake pressure - excess air ratio has also impact on the exhaust back pressure caused by the turbocharger and consequently on the obtained brake efficiency. Additionally, the dual fuel combustion is influenced by natural gas mass fraction and start of injection of diesel fuel and the search for the optimal solution could be a challenging task. The method presented here enables the use of a single cylinder experimental engine in this search, while simultaneously taking into account the influences of the effects of a full engine system. The results showed that for the load range IMEP = 10-13 bar the optimal excess air ratio for obtaining the highest efficiency is between 1.5-1.65, and that in respect to natural gas (NG) mass fraction the favorable option is to use the highest NG mass fraction possible; in this case 95%. Also, it was noticed that although the average excess air ratio is high and diesel fuel mass low, the obtained NO_X emissions were above Euro VI limit for heavy duty engines and it was not possible to lower the NO_X emissions below that limit by further leaning of the mixture, because the impact of the NO_X formation in the spray was too strong.