Novel Geometry Reaching High Efficiency for Multiple Injector Concepts

Abstract

Heat losses are known to decrease the efficiency of CI engines largely. Here, multiple injectors have been suggested to shrink these losses through reduction of spray wall impingement. Studies on multiple injectors have proven the concept's heat transfer reduction but also highlighted the difficulty of using a standard piston bowl. This study proposes a two-injector concept combined with a flat bowl to reduce heat losses further. To change the spray pattern, the two injectors are injecting in a swirling motion while placed at the rim of the bowl. Four injection timings have been investigated using Reynolds-Averaged Navier-Stokes simulations. This computational method quantified the amount of heat loss reduction possible. A conventional single injector concept is compared to two injector concepts with a standard and flat bowl. A Double Compression Expansion Engine (DCEE) concept, based on a modified Volvo D13 single-cylinder engine, was the base for all simulations. The DCEE can re-use the residual exhaust energy for a second expansion meaning increased importance of reduced heat losses. Heat release effects were discarded in the evaluation as an explanation for the reduced heat losses in order to isolate the effects of the changed spray pattern. Results showed a decrease in heat losses by 25.1 % or 4.2 % of the fuel energy as well as an increased IMEP of 4.5 % or 1.9 % of the fuel energy. Together with the increased exhaust energy, results showed a possible total engine efficiency increase of 2.6 % using the DCEE concept. This work successfully proves the benefits of using two injectors with a flat bowl over a standard bowl and the conventional one-injector strategy.

Isobaric Combustion for High Efficiency in an Optical Diesel Engine

“…It is also seen that much of the combustion takes place close to the edge of the bowl, suggesting an increased heat transfer. Hot zones at the walls have been proven to increase convective heat transfer in previous studies [9,10]. A substantial portion of injector dribbling is also observed at 9-22 CAD ATDC.…”

“…Other concepts try to utilize the chamber air volume in a better way by enhancing the mixing. For instance, multiple injectors concepts, where two or three injectors are used [7,8], have demonstrated lower heat losses as hot combustion gases are kept away from the cylinder walls with this strategy [9,10]. The multiple-injector concept is reported to directly increase engine efficiency by 1.9 %-points [10].…”

Thermal Efficiency Comparison of Different Injector Constellations in a CI Engine

“…However, this lower flame/wall interaction was not confirmed and needs to be studied further. Other computational studies have confirmed the heat loss reduction using multiple injectors [14,15]. In these studies, CFD simulations were performed to investigate how two injectors can reduce heat losses and increase the efficiency of an HD CI engine.…”

Computational Fluid Dynamics Investigation on Multiple Injector Concepts at Different Swirl Ratios in a Heavy Duty Engine

“…Multiple injector concepts reduce the heat losses for compression ignition engines by low near-wall temperature gradients, a smaller wall area covered by hot gases, and reduced near-wall velocity and turbulence [8][9][10][11]. Studies suggest a 25 % heat loss reduction (at some load conditions without swirl) by placing two injectors at the rim of the piston bowl [12]. However, no study has been performed on how multiple injectors reduce heat losses at different swirl ratios.…”