Effect of Fuel Injection Timing During Negative Valve Overlap Period on a GDI-HCCI Engine

Abstract

Gasoline Direct Injection Homogeneous Charge Compression (GDI-HCCI) combustion is achieved by closing early the exhaust valves for trapping hot residual gases combined with direct fuel injection. The combustion is chemically controlled by multi-point auto-ignition which its main combustion phase can be controlled by direct injection timing of fuel. This work investigates the effect of single pulse injection timing on a supercharged GDI-HCCI combustion engine by using a four-stroke single cylinder engine with a side-mounted direct fuel injector. Injection of primary reference fuel PRF90 under the near-stoichiometric-boosted condition is studied. The fuel is injected during negative valve overlap (NVO) or recompression period for fuel reformation under low oxygen concentration and the injection is retarded to intake stroke for the homogeneous mixture. It is found that the early fuel injection in NVO period advances the combustion phasing compared with the retarded injection in the intake stroke. Noticeable slower combustion rate from intake stroke fuel injection is obtained compared with the NVO injection due to charge cooling effect. Zero-dimensional combustion simulations with multiple chemical reaction mechanisms are simulated to provide chemical understanding from the effect of fuel injection timing on intermediate species generations. The species such as C2H4, C3H6, CH4, and H2 are found to be formed during the NVO injection period from the calculations. The effects of single pulse injection timings on combustion characteristics such pressure rise rate, combustion stability, and emissions are also discussed in this study.

Combustion chamber geometry and fuel supply system variations on fuel economy and exhaust emissions of GDI engine with EGR

“…CO2 emission is decreased at low speeds but higher at high speed [6]. The high peak pressure, temperature and NOx emission were reduced by using external dilution and two pulse injections [7].…”

Influence of piston crown shape with different positions of spark plug and fuel injector, %EGR, and fuel system control on emissions from modified GDI engines compared with a base diesel engine

“…Direct fuel injection during negative valve overlap period enables the auto-ignition enhancement species; fuel reforming could play role in advancing main combustion phase and shorter burn duration that lead to peak thermal efficiency at 41%. The high peak pressure, temperature and NOx (oxides of nitrogen) emission were decreased due to external dilution and split injections (Ratnak et al 2018).…”