Alcohol fuels for spark-ignition engines: Performance, efficiency and emission effects at mid to high blend rates for binary mixtures and pure components

Abstract

The paper evaluates the results of tests performed using mid-and high-level blends of the low-carbon alcohols, methanol and ethanol, in admixture with gasoline, conducted in a variety of test engines to investigate octane response, efficiency and exhaust emissions, including those for particulate matter. In addition, pure alcohols are tested in two of the engines, to show the maximum response that can be expected in terms of knock limit and efficiency as a result of the beneficial properties of the two alcohols investigated. All of the test work has been conducted with blending of the alcohols and gasoline taking place outside the combustion system, that is, the two components are mixed homogeneously before introduction to the fuel system, and so the results represent what would happen if the alcohols were introduced into the fuel pool through a conventional single-fuel-pump (dispenser) approach. While much has been written on the effect of blending the light alcohols with gasoline in this way, the results present significant new findings with regard to the effect of the enthalpy of vaporization of the alcohols in terms of particulate exhaust emissions. Also, in one of the tests, two mid-level blends are tested in a highly downsized prototype engine -these blends being matched for stoichiometry, enthalpy of vaporization and volumetric energy content. The consequences of this are discussed and the results show that this approach to blend formulation creates fuels which behave in the same manner in a given combustion system; the reasons for this are discussed. One set of tests using pure methanol alternately with cooled exhaust gas recirculation and with excess air shows a significant increase in thermal efficiency that can be expected as the blend level is increased. The effect on nitrous oxide emissions is shown to be similarly beneficial, this being primarily a result of the enthalpy of vaporization of the alcohol cooling the charge coupled with the lower adiabatic flame temperature of the alcohol. Whereas it is normally a beneficial characteristic in spark-ignition combustion systems, one disadvantage of a high value of enthalpy of vaporization is shown in another series of tests in that, in admixture with gasoline, it is a driver on flash boiling of the hydrocarbon component in the blend in direct injection combustion systems. In turn, this causes the particulate emissions of the engine to increase quite markedly over those of ethanol-gasoline blends at the same stoichiometry. The paper shows for the first time the dichotomy of the potential efficiency improvement with the challenge of particulate control. This effect poses a challenge for the future introduction and use of such high blend rate fuels in engines without particulate filters. Although it must be stated that the overall particulate emissions of the methanolgasoline blend are lower than for gasoline, the effect is only present at extremely low load, and that there is a likelihood that particulate filters will be adopted in production vehicle anyway...

A Review of Particulate Number (PN) Emissions from Gasoline Direct Injection (GDI) Engines and Their Control Techniques

“…When blended with gasoline, methanol reduces the final boiling point of the fuel, potentially promoting spray evaporation (and hence reducing PN emissions) however the increased ∆H vap and high volatility (leading to possible flash evaporation) may lead to poor mixture preparation and potentially higher levels of PN emissions. With such a mixed effect, as might be expected, studies on PN emissions from methanol-gasoline blends have again showed mixed results [141,[152][153][154].…”

“…E5 (up to 5% by volume of ethanol in gasoline) blends are ubiquitous in Europe, with E10 and E15 common in the USA; E85 is also common, although requiring vehicles that have been specially adapted (so-called flex-fuel vehicles); E100 is common in Brazil [136,137]. A number of recent studies on the influence of oxygenated fuel blends on PM emissions from GDI engines have been reported [1,85,114,[138][139][140][141]. Typically oxygenated fuels have higher vapour pressures, significantly higher ∆H vap (kJ/kg stoichiometric mixture), and significantly lower LHVs compared to gasoline.…”

Methanol as a fuel for internal combustion engines

“…Alcohol blending can take the form of low-, mid-and high-level blends, for which there is no formal definition, but which Turner et al considered to be up to 15% by volume (low), 15-30% (mid) and over 30% by volume (high) [57]. Israel recently adopted an M15 standard [58].…”

Experimental Investigation of Diluents Components on Performance and Emissions of a High Compression Ratio Methanol SI Engine

“…As an alternative fuel with great application potential, many researchers have tested methanol on spark ignition (SI) engines and compression ignition (CI) engines or other engines work with new combustion strategies. Turner [6] et al tested methanol-gasoline blends on an SI engine, they figured that methanol provides a much higher knock limit and gives great improvements in thermal efficiency compared with pure gasoline. Avinash et al [7] found methanol can increase brake thermal efficiency (BTE) and made a lower emission of NO x , CO and smoke opacity for its higher latent heat of evaporation between NOx emissions and fuel consumption.…”

“…Ladommatos et al [21][22][23][24] also pointed out that dilution effect of EGR is the dominate cause of the NOx reduction through experiments on a diesel engine. According to Turner, methanol allows using EGR for lean burn to a higher degree than gasoline on a high-CR engine, so methanol is a suitable fuel for high-CR SI lean burn engine [6].Although it has been proved that EGR can improve engine performance, the specific role of its internal components, it is not clear which is required to study further. Exhaust gas contains nitrogen (N 2 ), carbon dioxide (CO 2 ) and argon (Ar).…”