Inverted Reactivity Controlled Compression Ignition (iRCCI) with Methanol Fuel & Reactivity Enhancers

Reactivity Controlled Compression Ignition (RCCI) is a low temperature combustion regime that has demonstrated ultra-low NOx and soot while achieving high thermal efficiency. RCCI uses a low reactivity premixed charge which is ignited via direct injection of a high reactivity fuel. The aim is to create a nearly homogeneous charge but maintain control over the combustion timing via the ratio between the premixed and direct injected fuel, hence controlling global reactivity via reactivity gradients in-cylinder. RCCI combustion with gasoline as the premixed fuel and diesel as the high reactivity fuel has shown good combustion timing controllability. However, RCCI with alcohol fuels, in which pure alcohol is the low reactivity premixed fuel and the alcohol doped with a reactivity enhancer is the direct injected high reactivity fuel, has shown a lack of control over the combustion timing, which is undesirable. This study attempts to regain control over the timing of combustion by using the high reactivity fuel (alcohol/reactivity enhancer) as the premixed charge while direct injecting the low reactivity fuel (pure alcohol). Thus, this strategy is referred to as inverted RCCI (iRCCI) as the fuel streams are reversed from conventional RCCI operation. The charge cooling effect of the direct injected alcohol results in reactivity stratification in-cylinder by reducing the local temperatures where the directed injected fuel is targeted and regains control over combustion phasing through the ratio of the premixed charge and direct injected fuel. Methanol was used as the base fuel and blended with a commercial reactivity improver, di-tert-butyl peroxide (DTBP). These blends of fuel were tested under lean premixed combustion conditions with neat methanol as the direct injected fuel and methanol/DTBP blends as the premixed charge. Computational simulations were run to demonstrate that the iRCCI fueling strategy has some level of combustion timing controllability. The level of combustion timing control authority is not as strong as conventional RCCI with premixed methanol and direct injected diesel fuel but is dramatically improved over operation with premixed methanol and direct injected methanol/DTBP.