Influence of Injection Timing on Equivalence Ratio Stratification of Methanol and Isooctane in a Heavy-Duty Compression Ignition Engine
CO2 is a greenhouse gas that is believed to be one of the main contributors to global warming. Recent studies show that a combination of methanol as a renewable fuel and advanced combustion concepts could be a promising future solution to alleviate this problem. However, high unburned hydrocarbon (UHC) and carbon monoxide (CO) emissions can be stated as the main drawback in low load operations when using methanol under advanced combustion concepts. This issue can be mitigated by modifying the stratification of the local equivalence ratio to achieve a favorable level. The stratifications evolved, and the regimes that can simultaneously produce low emissions, and high combustion efficiency can be identified by sweeping the injection timing from homogeneous charge compression ignition (HCCI) to partially premixed combustion (PPC). Understanding how the stratification of the local equivalence ratio for methanol evolves during the sweep is essential to gain these benefits. Thus, the current experimental work has been carried out to investigate the influence of injection timing on the emissions and combustion efficiency of methanol. The experimental work was performed with a single cylinder heavy-duty engine, run at ~4 bar gross indicated mean effective pressure, and speed at 1200 rpm. Single injection strategy was applied, and the injection timing was swept from -140o to -15o aTDC. During the sweep, the combustion phasing (CA50) was kept at ~3o aTDC by tuning the intake temperature. To understand the impact of fuel properties along the sweep, isooctane was used and compared with methanol. Additionally, a numerical simulation was used to explain how the stratification of the local equivalence ratio evolved and impacted the combustion characteristics, emissions, and combustion efficiency during the whole sweep.