Two simultaneous strategies have been used in this work to reduce the diesel engine emissions. First, using novel manifold designs to generate strong turbulence and improve the fuel-air mixing inside the cylinder. The second strategy is the usage of alternative fuels, namely Gas-To-Liquid (GTL) fuel and its blends with diesel fuel. In this study, six new spiral-helical manifolds designs have been tested, which could be divided into two groups. The first group is m(2.6,30,1t), m(2.6,30,2t), m(2.6,330,3t) and m(2.6,30,4t) which contains manifolds that have the same inner diameter (2.6 cm), same outlet angle (30°), but different number of spiral turns (1t, 2t..etc). The second group is m(2.1,30,3t), m(2.6,30,3t) and m(2.9,30,3t) which contains the same parameters but different inner diameters. It should be mentioned that the outlet angle of all manifolds has been tested in previous investigations [18, 52] and 30° showed the best performance.

The results of the current study showed that the highest pressure and heat release achieved by manifold m(2.6,30,1t) for the blended diesel-GTL fuel. It was observed that the heat release rate decreases with the increase in number of turns. The lowest pressure raise rate was recorded for the combination of m(2.6,30,1t) and diesel fuel. Same combination also reduced the pressure raise rate (dP/dθ) by about 24% compared to the normal manifold. The bsfc for all fuels and m(2.6,30,1t) were almost the same as the normal manifold. For the emissions, NO emissions were reduced by about 25% compared to normal manifold when m(2.6,30,4t) and GTL are used. On the other hand, the normal manifold recorded the least NO emissions for the other fuels. The manifold m(2.6,30,1t) recorded slightly higher NO emissions compared to the normal manifold for all fuels. The total particulate matters (PM) were the lowest for m (2.6,30,1t) and normal manifold in case of diesel fuel. In general, It was found that the combination of m(2.6,30,1t) with diesel fuel gave the optimum performance among all manifolds, while using m (2.6,30,4t) with GTL fuel produced low emission levels.

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