An Experimental Study on Smoke Reduction Effect of Post Injection in Combination With Pilot Injection for a Diesel Engine

Abstract

With the universal utilization of the common-rail injection system in automotive diesel engines, the multistage injection strategies have become typical approaches to satisfy the increasingly stringent emission regulations, and especially the post injection has received considerable attention as an effective way for reducing the smoke emissions. Normally the post injection is applied in combination with the pilot injection to restrain the NOê missions, smoke emissions, and combustion noise simultaneously, and the pilot injection condition affects the combustion process ofthe main injection and might affect the smoke reduction effect of the post injection. Thus this study aims at obtaining the post injection strategy to reduce smoke emissions in a diesel engine, where post injection is employed in combination with pilot injection. The experiments were performed using a singlecylinder diesel engine under various conditions of pilot and post injection with a constant load at an IMEP of 1.01 MPa, flxed speed of 1500 rpm, and NO^ emissions concentration of ¡50 ± 5 ppm that was maintained by adjusting the EGR ratio. The injection pressure was set at 90 MPa at first, and then it was varied to 125 MPa to evaluate the effects of post injection on the smoke reduction in the case of higher injection pressure. The experimental results show that small post injection quantity with a short intei-val from the end of main injection causes less smoke emissions. And larger pilot injection quantity and later pilot injection timing lead to higher smoke emissions. And then, to explore and interpret the smoke emissions tendencies with vaiying pilot and post injection conditions, the experimental results of three-stage injection conditions were compared to those of two reference cases, which only included the pilot and main injection, and the interaction between main spray flames and post sprays was applied for analysis. Based on the comparative analysis, the larger smoke reduction effect of post injection was obsei-ved with the larger pilot injection quantity, while it is not greatly influenced by pilot injection timing. In addition, the smoke emissions can be reduced considerably by increasing the injection pressure, however the smoke reduction effect of post injection was attenuated. And all of these tendencies were able to be interpreted by considering the intensity variation ofthe interaction between main spray flames and post sprays.

Analysis of Mixture Formation Process in a Diesel Engine with Post Injection

“…The total injection quantity was set at 33 mm 3 /cycle, where the IMEP was approximately 1.0 MPa. On the basis of the previous study [14], the pilot injection quantity was set at 6 mm 3 /cycle to realize the entirely mixing-controlled combustion of the main spray and a relatively high smoke level for easy detection of the soot-reduction effect of post injection. The intake manifold pressure and temperature were adjusted to 120 kPa and 35°C.…”

Optimization of diesel fuel injection strategies through applications of cooperative particle swarm optimization and artificial bee colony algorithms

“…Each subswarm searches a small section of the design space using the best results from other subswarms only changing its assigned variables. If any subswarm SN improves its best solution (G best ), this is communicated to other subswarms using a context vector (X context ) given by equation (7). The fitness of the context vector can only improve with each algorithm iteration, which can lead to the algorithm getting stuck in local minimums without the ability to climb out and move to better spaces in the design space.…”

“…6 Careful control of the pilot quantity is needed as large pilots can take increasing amounts of oxygen away from the main injection. 7 Additional pilots can be added to the compression stroke to promote premixing, but the increased heat of vaporization of diesel fuel can make it challenging to prevent wall wetting. 5 Small post injections increase the burning rate of the main injection fuel when timed near to the main injection.…”

Effects of multiple injections on combustion and emissions in a heavy-duty diesel engine at high load and low speed

“…In a heavy-duty diesel engine, the effects of injection strategies on emissions were investigated by many researchers, [3][4][5][6][7][8][9][10][11] it was found that small post injection mass with a short main-post injection interval produces less smoke; 6 dramatic soot reduction without a NO x penalty can be achieved by injecting enough fuel in post injection at an appropriate EGR rate; 8 there is a tradeoff relation between carbon monoxide (CO), hydrocarbon (HC), and NO x emissions with crank angle intervals increasing, lowest particulate matter emissions appear at middle post injection timing; 9 proper post injection may help in soot oxidation; 10 more CO formation and less HC emission are obtained during multiple injection combustion process, and simultaneous reductions of 58.7% and 25%, respectively, for NO x and soot can be achieved. 11 A new concept of variable injection pressure of multiple injections was proposed by Poorghasemi et al, 12 and it was found that increasing post injection pressure can reduce the soot emission significantly while the NO emission is in control.…”