# Advances in Diesel-LNG Internal Combustion Engines
## 2 Results
### Computational Proof of Concept of Novel Diesel-LNG ICE Designs
This model permits to define the Ignition Delay, that is the delay in crank-angle degrees between the start of injection and the start of combustion, the Premixed Fraction, that is the fraction of fuel that mixes before the start of combustion and burns in the premix portion of the Wiebe function, the Tail Fraction, that is the fraction of fuel that burns beyond the main diffusion burn, the Premixed Duration, that is the duration in crank-angle degrees of the premixed burn, the Main Duration, that is the duration in crank-angle degrees of the main diffusion burn. The main duration excludes the first and the last parts of the area under the main burn curve, the Tail Duration, that is the duration in crank-angle degrees of the tail burn curve, and finally the Premixed, Main and Tail Exponents of the Wiebe curves for the premixed burn, the main burn, and the tail burn. These parameters are empirical values obtained from measurements of similar ICEs tabulated vs. BMEP and speed. The definition of the combustion model is coupled to the definition of the multi-event injection profile, which includes pre/pilot and main injections. This model is set up for the diesel-only operation. In the case of the 2F diesel-LNG, it is simply assumed that the diesel pre/pilot amounts are the same as the diesel only, and only the main LNG replaces the main diesel. As only one fuel is considered in the model, the pre/pilot diesel injection is replaced by an LNG injection of equivalent energy content, the same as the main diesel injection. As the controller adjusts the total mass of fuel injected to match the requested BMEP at every speed, there are minor differences between the energy inputs of the diesel and the diesel-LNG models for the same BMEP and speed operating point. While the accuracy may certainly be improved by adopting a model accounting for chemical kinetics and multiple species, this approach not only needs more computational effort, it also needs substantial experimental support to tune and confirm the model. Not considered here is the possibility in the real ICE to inject some LNG prior or contemporary to the diesel pre/pilot, which may increase the premixed combustion, and produce conditions within the chamber more favorable for the LNG main injection fuel to burn diffusion controlled. Finally, in computing the LNG replacement fuel, it is simply assumed that the amount of the diesel fuel injected during the pilot/pre-injections is about constant in mass, and thus a linear function of the engine speed. Experimentally, this assumption is correct at medium-to-high loads and high speeds, while in the low speed and low loads region the amount the diesel fuel introduced with the pilot/pre-injections may be larger. Figures 7 and 8 present the computed \(\eta\) and \(\lambda\) maps of the super turbocharged and turbocharged diesel ICE, while Figures 9 and 10 present the \(\eta\), \(\lambda\), and LNG energy/total fuel energy maps of the super turbocharged and turbocharged diesel-LNG ICE. The advantages of the super turbocharger (or electrically assisted turbocharger) are clear at low speeds, where higher BMEP is made possible, and at high speeds high loads, where the extra energy at the turbine is not waste gated but recovered. Not included in the simulations, that are only steady-state, are the further advantages during a transient, both accelerations, as the turbo-lag is completely canceled supplying the extra energy needed by the compressor, and during decelerations, where the extra energy delivered by the turbine is also recovered. Concerning diesel only, the diesel-LNG ICEs provide slightly better \(\eta\), both in the super-turbocharger and turbocharger versions, running with smaller \(\lambda\) at the higher loads. The replacement LNG energy may be as high as 98% of the total fuel energy, at the higher loads and speeds. It is well above 90% up to 8 bar BMEP. The LNG energy reduces with the load and the speed.