Fig. 7 Relationship between nozzle hole angle φ and piston
Fig. 8 Test results of changing injection timing when low NOx technology is employed
For example, the comparison in terms of the same fuel consumption, shows the reduction of NOx emission by approximately 40%. It is believed that the NOx emission is reduced by reducing the zone of the air excess ratio λ=1 by the impingement with the wall surface, and by promoting the mixing of the combustion portion with air, and further, the soot generated in the combustion of the rich mixture fuel-air mixture of the air excess ratio of λ＜1 due to the impingement with the wall surface is re-burned by the swirl, and the soot to be finally discharged is reduced in quantity.
5. Conclusion
In this study, the low NOx concept obtained with the compact high speed engine was developed for the medium speed engine, the low NOx technology was proposed by taking into consideration the difference in the combustion phenomenon between the compact high speed engine and the medium speed engine for the specific technology to realize the concepts, and its effectiveness is confirmed with the single cylinder engine for study. As a result, the conclusion is obtained as follows.
(1) The concept on the low NOx diesel combustion focusing on the initial stage of combustion and the middle stage of combustion high in combustion temperature, is to reduce the zone of the stoichiometric combustion of the fuel-air mixture (λ=1), and to promote the mixing of the combustion portion with air.
(2) The low NOx technology of the medium speed engine based on the above-described concept is to obtain the direction of injection in which the distance from the nozzle to the wall surface is shortened in order to impinge the fuel with the wall, surface of the combustion chamber before forming the fuel-air mixture of λ=1, and to obtain the appropriate swirl to promote the mixing of the combustion portion with air.
(3) The trade-off relationship between the fuel consumption and NOx is greatly improved by the low NOx technology, and the NOx emission is reduced by approximately 40% with the same fuel consumption.
(4) The soot generated in the combustion of the rich fuel-air mixture due to the collision with the wall surface is considered to be re-burned (oxidized) by the swirl, and the exhaust smoke was also improved by the low NOx technology.
References:
(1) S. Yoshikawa. et al., “The Development of Low NOx Emission Diesel Engine”, CIMAC (1995), D28
(2) J. F. Alcock and W. H .Scott., “Some More Light on Diesel Combustion”, Pnoc, I. Mech. E., No.5 (1962), 179-200.
(3) Y. Wakuri. et al., “Studies of the Penetration of Fuel Spray in a Oiesel Engine”, Bulletin of the JSME, Vol. 25, No, 156, 1959, 820.
