Comparison and Impacts of LH2 to Conventional Jet A-1 Turnarounds

3.5 Comparison and Impacts of LH2 to Conventional Jet A-1 Turnarounds In addition, there is the question of what happens to the vaporised H2 that is fed into the tank. This GH2 must be recovered, as otherwise, the pressure in the aircraft tank would rise, which would lead to the undesired temperature increase of the fluid and density reduction, as described above. Relating these results back to the aircraft design, the volume of the aircraft tank is determined from these tank conditions, which has a considerable influence on the mass and hence the performance of the aircraft, see Section 4.1.

However, a high mass flow of vaporised H2 to be removed would be reflected in the recovery line’s dimensions. High velocities should also be avoided because phenomena such as resonances and pressure shocks should be prevented to limit the flow-related loads on the components.

3.5 Comparison and Impacts of LH2 to Conventional Jet A-1

3.5 Comparison and Impacts of LH2 to Conventional Jet A-1 Turnarounds Due to the different procedures of LH2 and Jet A-1, the intersection of the same refuelling energy results after 11.5 min with one Jet A-1 hose and 20.5 min with two hoses. To classify these results with purging, the refuelled mass of Jet A-1 with one hose after 11.5 min corresponds to 8425 kg and with two hoses after 20.5 min to a mass of 39,180 kg. For comparability, the horizontal dashed lines are drawn as maximum tank capacity for an A320 and A350 in Figure 3.11.

It is thereby evident that in a refuelling process with the maximum fillable volume, LH2 has a time advantage. With smaller volumes and hence shorter ranges, on the other hand, the refuelling times are similar. To better analyse this behaviour, three scenarios are presented in the following section through a Gantt chart. The conservative approach is chosen that the purging process must occur to the full extent. For the use of a clean break disconnect, the time duration of 3 min can be deducted from the results. The different scenarios handle different refuelling masses and an aircraft configuration with tank pods on the wings.

Figure 3.13 shows the Gantt chart for an A320-like aircraft refuelling at the maximum tank volume. Here, the previous hypothesis applies that the aircraft have the same efficiency and performance and can fly the same distance with identical amounts of energy. As a result, the mass of LH2 can be determined by the ratio of the calorific values. It follows that the H2 mass is lower by a factor of 2.8. A time advantage of 3 min is shown with the Gantt diagram in Figure 3.12 when refuelling Jet A-1 the equivalent energy amount.

Figure 3.12: Gantt chart for Jet A-1 refuelling of 15,000 kg with one deck hose; initial volume flow of 1800 l/min

Figure 3.13: Gantt chart for LH2 refuelling of 5350 kg

3.5 Comparison and Impacts of LH2 to Conventional Jet A-1 Turnarounds In contrast, scenario 2 compares a refuelling volume for a 500 NM mission. Figure 3.14 shows the Gantt diagram for this purpose. Due to the small volume, the advantage of LH2 is no longer present, but the refuelling time is in the same order of magnitude. Based on the findings from Section 2.4, the advantage in refuelling time is of no benefit, since in most cases, refuelling is not on the critical path of the turnaround. In other words, an extension of the refuelling time by a few minutes would not lead to any noticeable effects of the turnaround process.

Figure 3.14: Gantt chart for LH2 refuelling for a 500 NM mission, excluding reserves; fuelled mass of LH2 1000 kg; corresponding refuelling time for 500 NM mission of Jet A-1 is 7 min

The previous consideration of the refuelling time is independent of the aircraft configuration and the position of the LH2 tank in the aircraft. In scenario 3, the comparison of the refuelling time for a 1500 NM mission of an aircraft with the tanks mounted at the wings will be investigated.

A comparable aircraft configuration can be found inSilberhorn et al. [129]. The comparison will be between the possibility of parallel refuelling with one pod connected to feed the other pod and the possibility of sequential refuelling. Figure 3.15 shows the Gantt chart for parallel refuelling in this comparison situation.

Figure 3.15: Gantt chart for parallel LH2 refuelling for a 1500 NM mission, excluding reserves;

fuelled mass of LH2 2500 kg; corresponding refuelling time for 1500 NM mission of Jet A-1 is 10 min

3.5 Comparison and Impacts of LH2 to Conventional Jet A-1 Turnarounds

Figure 3.16: Gantt chart for sequential LH2 refuelling two podded tanks; refuelling for a 1500 NM mission, excluding reserves; fuelled mass of LH2 is 2500 kg

In sequential refuelling, where the pods are filled consecutively, the refuelling process takes 11 min longer than in the parallel case, see Figure 3.16. This difference is because each sub-process in the refuelling has to be performed twice, and the vehicle has to drive around the aircraft once.

The refuelling process for a 1500 NM mission on Jet A-1 would take 10 min with one hose.

Considering the special aircraft configuration, the refuelling process in sequential operation takes 12 min longer than Jet A-1. The parallel process, on the other hand, takes 1 min longer than Jet A-1. However, in the parallel refuelling process, the cooling time is independent of the pipe’s length between the pods. This assumption is only valid if this connecting pipe is short or kept at cryogenic temperatures permanently. However, the case of a required cooling in the refuelling process cannot be appropriately considered, as the chill down time’s analytical solution is independent of the pipe length, see Section 3.2.3.

Cash Operating Costs of Liquid Hydrogen Fuelled-Aircraft

An extension of the refuelling time due to a particular LH2 aircraft configuration can therefore occur. However, as described in Section 2.4, the effects on the turnaround will only be weak.

As a result, a change in the refuelling time has only a minor effect on the aircraft’s utilisation.

Conversely, the profitability of the aircraft and thereby the market existence hardly changes. In Figure 3.17, this finding is illustrated by the COCs. It becomes clear that for longer turnaround times, there is no linear correlation on the COCs. In connection with the flight range, it can be seen that the influence of the turnaround time on the costs decreases with increasing flight range. This behaviour is due to the application of the stochastic values from Figure 2.20. A longer turnaround time does not affect the utilisation or costs for longer flight distances since the aircraft can compensate for the delay during the flight. For short-haul flights, this compensation is only possible to a limited extent, as the turnaround time accounts for a much larger percentage of the available time.

3.6 Losses and Cost Adaption Due to Refuelling With Liquid Hydrogen

Figure 3.17: COCs for a 180-passenger aircraft versus the turnaround time; additional dependence on the flight distance and by differentiating the energy carrier from LH2 or sustainable aviation fuel

To classify the calculated COC values, the costs for a comparable aircraft with sustainable aviation fuel produced renewably by PtL are plotted in Figure 3.17. The curves of the different energy sources behave in the same way, but there is an offset between them. This is because PtL requires more energy for production, and thus the fuel price is higher. The price for LH2 in this diagram is assumed to be 29.15 EUR/GJ and for PtL 35.6 EUR/GJ [130]. Thus, the 22 % price difference between the fuels is only reflected in the COCs in a weakened form.

Due to the low fuel price, LH2 has an advantage when considering the COCs. However, considering the DOCs, in which capital costs are also taken into account, would lead to PtL causing the lower costs. This is because the development costs for an LH2-powered aircraft would increase significantly compared to PtL.

3.6 Losses and Cost Adaption Due to Refuelling With Liquid