Analysis of Low and High Temperature Heat Release in Dual-Fuel RCCI Engine and its Relationship with Particle Emissions

This study presents the influence of low-temperature heat release (LTHR) and high-temperature heat release (HTHR) on the combustion and particle number characteristics of the RCCI engine. The study investigates the relationship between the amount of LTHR, HTHR, and particle number emission characteristics. In this study, gasoline and methanol are used as low reactivity fuel (LRF), and diesel is used as a high reactivity fuel (HRF). The LRF is injected into the intake manifold using a port-fuel injection (PFI) strategy, and HRF is directly injected into the cylinder using a direct injection strategy. A particle sizer is used to measure particle emission in size ranging from 5 to 1000 nm. Firstly, the LTHR and HTHR are analyzed for different diesel injection timing (SOI) for RCCI operation. Later, the variation of particle emissions with LTHR and HTHR is characterized. Additionally, empirical correlations are developed to understand the relation between the LTHR and HTHR with particle emission. Two-staged auto-ignition of charge has been observed in RCCI combustion. Results depict that LTHR varies with diesel injection timing and the phasing of HTHR depends on the amount and location of LTHR. Results also showed that HTHR and LTHR significantly influence the formation of particle number concentration in RCCI combustion. The developed empirical correlation depicts a good correlation between diesel SOI and the ratio of HTHR to LTHR to estimate total particle number concentration.

The Interaction Between the Pilot Diesel and Main NG Injection in an HPDI Engine

High Pressure Direct Injection (HPDI) is a promising combustion concept for the medium- to heavy-duty industry to combat climate change. It uses a pilot diesel injection to ignite the main fuel consisting of Natural Gas (NG). Both fuels are injected directly in the combustion chamber using a dedicated HPDI injector. A significant reduction in carbon dioxide and Particulate Matter is achieved due to the use of the low carbon fuel NG. It is seen in literature that a small change in pilot injection can have profound consequences for the HPDI combustion. This research investigates the interaction between the pilot diesel and main NG injection. A relevant Computational Fluid Dynamics (CFD) simulation environment is setup for this purpose. It is observed that the main NG injection needs a certain pilot trigger to ignite. Furthermore, local conditions are derived to investigate driving factors of the ignition of NG on a fundamental level. A homogeneous reactor model is used to study Ignition Delay (ID) behavior by varying the initial temperature as well as concentrations of radicals H and OH. It is observed that both factors influence the ID. The initial temperature has to be higher than 1110 K in order to ignite the NG under enginelike conditions. It is also observed that species mole fractions H or OH encountered in the CFD simulation can reduce the ID up to 5.5 crank angle degrees at a speed of 1400 RPM.