Study of Hydrogen Port Injection Si Engine

Abstract

The rapidly growing energy demands and environmental concern of transportation sector, primarily powered by hydrocarbon-based fossil fuelled IC engines are looking for a sustainable energy economy. Among the alternates, the carbonless hydrogen is the most suitable fuel that can be adopted with minute changes. Most of the hydrogen properties, such as a high autoignition temperature and a high-octane rating, find it suitable for the SI engine. However, low volumetric energy content and higher diffusivity limit power output. Hence, an increased CR helps overcome the volumetric losses. Besides, equivalence ratio (ϕ) plays a vital role in SI engines. Another primary concern is NOx, which worsens by increasing CR and ϕ. Many researchers concluded that retarded ignition timing (IT) reduces NOx emissions. However, it is not explicit about falling under the permissible limit. Hence, effective NOx reduction tool EGR is preferred, and the power drop due to EGR can be improved by boosting MAP. The experimental study is conducted in two stages under WOT conditions at three engine speeds, 1400rpm, 1600rpm and 1800rpm for hydrogen PFI SI engine. In the first stage, the effect of varying CR from 10 to 15 at various ϕ from 0.4 to 1.0, keeping the IT fixed at 20ºCA bTDC is studied as first phase. An optimal operating parameter is decided based on the trade-off between BTE and NOx emissions. Later, the effect of variable IT from 24ºCA bTDC to 14ºCA bTDC is studied at the selected CR for ϕ varying ±0.05 from ϕ decided from first phase. The optimised IT and ϕ are decided for the next stage. Various EGR ratios (from 5% to 15%) at variable MAP (from N/A to 110kPa) are studied for NOx control at minimal power loss in the last stage. BP and BTE, ηvol dropped rapidly. At high CR (>13), a rich mixture (ϕ≥0.9) has adverse effects, reducing BTE. Pmax and HRRmax are increased by increasing CR for ϕ<0.9. While, for ϕ=0.9 at 1800rpm, they are nearly static for CR14 and CR 15, at ϕ=1.0, dropped slightly at CR 15. CA10 was reduced with increasing CR and ϕ, while CA10-90 shortens with increasing CR for ϕ<0.8. CA10-90 is increased slightly for ϕ≥0.8 after CR13. CoVIMEP was reduced by increasing CR for ϕ≤0.8, while after ϕ=0.8, there is a slight increase noticed after CR13. The specific NOx emissions are increased with ϕ, CR and speed. However, for ϕ=1.0 at CR15, NOx emission is dropped insignificantly. CR14 has the best trade-off between BTE and NOx at ϕ=0.7/0.8. Delaying IT improved BP and BTE till maximum and then deteriorates at any speed and ϕ. The optimal IT retards with increasing ϕ and speed. CA10 is reduced, while CA10-90 reduces till certain IT. The IT of minimum combustion duration is retarded with increasing ϕ and speed. Pmax and HRRmax are reduced by retarding IT, while the rate of rise in CP and HRR before TDC is increased. Tmax is reduced by retarding IT, and CoVIMEP is reduced till a certain IT. EGT is increased gradually with IT retard at low speed and low ϕ, and rapidly at high speed. Retarding IT reduces NOx emissions. The rate of reduction increases with increasing ϕ and speed. 16ºCA bTDC, IT at ϕ=0.8, is efficient for controlling NOx moderately without BTE compromise. BP and BTE are improved for low EGR (5-7.5%) but dropped rapidly with a further increase in EGR. ηvol is reduced continuously with EGR. Boosting MAP increases BP, BTE, and ηvol; even at high EGR, power is regained by 5% by boosting MAP to 110kPa. CP, and HRR are increased slightly for low EGR but dropped rapidly with higher EGR. Boosting MAP increased CP and HRR due to large fuel supplied to maintain ϕ. Similarly, increasing ηvol supplies more air, increasing CA10, and a large fuel mass increased CA10-90. A slight EGR has reduced CA10 and CA10-90, but a higher EGR deteriorated combustion. Similarly, Tmax and EGT increased with EGR up to 5%. A net 34% NOx reduction is observed at MAP 110kPa by 15% EGR than N/A conditions. The hydrogen-fuelled SI engine competes equally with the gasoline SI engine at a relatively higher CR, retarded ignition, and has efficient NOx control by EGR implemented parallelly with MAP boost. Further, based on the current findings, research can be advanced in a more complicated but efficient technology, such as high-pressure hydrogen DI SI system, variable MAP control through supercharging, and split high-pressure hydrogen DI.