GTL fuel in a dedicated vehicle - exploration of the full emissions reduction potential

摘要

In any discussion of a future fuels portfolio, GTL (Gas-to-Liquids) will play an important role. This stems from its ability to act as an enabler in the key areas of diversification of the energy supply and reduction in road transport emissions [1]. The start of production from Sasol's GTL plant Oryx, and the current construction of the world's largest GTL plant, Shell's Pearl plant in Qatar, signals that GTL fuel is no longer an option for the distant future, but that significant volumes will be reaching the market in the short to medium term. GTL fuels have market potential when used either neat or in blends with conventional diesel fuel. In those areas, that are sensitive to air quality issues (e.g. inner cities), the use of neat GTL fuel in dedicated fleets is an attractive option, because of the emission reduction effect that GTL fuel can have. The progression from using neat GTL fuel in conventional vehicles towards the possibilities of optimizing engines specifically for GTL fuel is the natural next step. With this study, the full emissions reduction potential of GTL fuel in a dedicated vehicle was explored. The investigation followed a step-wise approach: firstly optimizing the calibration to GTL fuel, then secondly both hardware and calibration undergo an optimization. The full emissions reduction potential of GTL fuel was investigated by setting different optimization goals: Minimization of NO_x emissions and minimization of fuel consumption, and thus CO_2 emissions. For both strategies, the vehicle was successfully optimized. Using GTL fuel and the software optimization, EU 5 emissions were achieved with a former EU 4 vehicle, and exhaust CO_2 emissions could be reduced by 10% with the minimum fuel consumption optimization goal (i.e. compared to the baseline vehicle fuelled with conventional diesel). With the additional optimization of the hardware (reduction of compression ratio and hydraulic flow of the injectors), a substantial reduction of local emissions was reached. Complementing these technical results, the feasibility of vehicles dedicated to GTL fuel are discussed. The first step, resulting in an optimized calibration, may lead to self-adapting vehicles that would enable a scenario of local mixed fuel supply, including GTL. The second step, however, with adapted engine hardware would not necessarily allow flexible fuelling with both GTL and conventional diesel. Thus, a guaranteed GTL fuel supply would be required, as indeed would be feasible in closed fleets. In conclusion, the full potential of GTL fuel has been explored when it is in combination with a dedicated engine. This has resulted in a better understanding of the maximum impact that alternative and clean fuels such as GTL fuel can have on emissions and fuel consumption.