An experimental and analytical investigation into the combustion characteristics of HCCI and dual fuel engines with pilot injection.

摘要

The combustion processes within Homogeneous Charge Compression Ignition (HCCI) and dual fuel engines with pilot liquid fuel injection were investigated both experimentally and analytically. An ISUZU 3KC1 engine with a swirl chamber was suitably modified, fitted with the developed necessary instrumentation and supporting data acquisition and calculation software systems. Also, a fully instrumented variable compression ratio single cylinder CFR engine made capable of operation on gaseous and liquid fuels mixtures was used for HCCI operation. In parallel with the experimental investigation, 3D predictive computational models were developed and applied to both the HCCI and dual fuel engine combustion systems. The models, based on the KIVA3 software, incorporate detailed chemical kinetics for the oxidation of hydrogen, n-heptane, and diesel fuel while accounting for the turbulence-chemistry interactions during combustion. Much of the results of the predictive models were validated against the corresponding experimental behavior.; The combustion characteristics and cyclic variation of an n-heptane and n-pentane fuelled HCCI CFR engine were examined. The effects of changes in compression and equivalence ratios, and the additions of nitrogen, carbon dioxide, and different gaseous fuels on n-heptane fuelled HCCI engine were investigated. The optimum values for the addition of N2, CO 2, and CH4 to produce higher power and reduce cyclic variation and the intensity of energy release in HCCI combustion were determined and found to depend on the intake mixture strength, the extent of any non-homogeneity, and the specific operational conditions.; The combustion characteristics of the modified ISUZU 3KC1 engine with a swirl chamber when operating as diesel or dual fuel engine were investigated. This included determining the effects of factors such as engine speed and the quantities of the pilot and gaseous fuels on engine performance, emissions, cyclic variation, and combustion noise. It was found that a minimum absolute quantity of diesel fuel is needed to achieve steady combustion and obtain high fuel conversion efficiency for a specific operational condition.; The results of the simulation of the combustion characteristics of n-heptane fuelled HCCI-CFR engine were in good qualitative and fair quantitative agreement with the corresponding experimental values. It was found, for example, that changes in the values of the combustion chamber wall surface temperature influence greatly the autoignition timing and its location within the chamber. For high chamber wall temperatures, autoignition takes place first at regions near to the cylinder surface and the quenching distance is reduced. The effects of the initial intake swirl, temperature and pressure, engine speed, compression and equivalence ratios, and the addition of diluents and gaseous fuels on the combustion characteristics of a hydrogen fuelled HCCI engine were examined. Also, the effects of injection timing and the quantity of hydrogen admitted on the combustion of a diesel/hydrogen direct injection Gardner dual fuel engine with a hemispheric piston crown were investigated through a series of simulations. Furthermore, the corresponding processes within the ISUZU 3KC1 diesel and diesel/methane dual fuel engines with a swirl chamber were examined in detail, and the influence of changes in engine speed, injection timing, and the quantity of diesel and gaseous fuels on combustion and performance were investigated. It was observed that an earlier autoignition can be obtained through injecting the pilot fuel into the small prechamber compared to the corresponding swirl chamber operation. Furthermore, through the early injection of a small pilot liquid fuel into the swirl chamber of the dual fuel engine, a two-stage HCCI combustion can be achieved which may reduce engine emissions and improve thermal efficiency.