Effects of Oxygenated Fuels on DI Diesel Combustion and Emissions

Abstract

Emissions from compression ignition (CI) engines are being placed under stricter regulations. The use of oxygenated fuels has been proposed as a means of complying with future emission levels. Previous research on oxygenates has suggested the presence of molecular oxygen within the fuel significantly reduces the formation of particulate matter (PM). The PM reduction is logarithmic and correlates with the weight percent of oxygen in the fuel and not with other properties such as chemical structure and volatility. However, many studies fail to correctly decouple the effects of oxygenates from other fuel properties that impact emission levels; such as cetane number, density, aromatic content, and volatility.Mechanisms responsible for changes in the combustion process and emissions were investigated with a matrix containing 14 fuels, addressing oxygenate proportionality, structure, volatility, equivalent structure without oxygen, and changes in the base diesel fuel. A scanning mobility particle sizer (SMPS) was used to evaluate changes in particle size distributions, in addition to gravimetric filter and oxides of nitrogen (NOx) measurements.Engine emissions tests were conducted using a Ricardo Hydra MK IV direct injection (DI) diesel engine. The sensitivity of engine operation parameters to intake temperature, load, injection timing, and ignition delay (ID) were evaluated with the baseline fuel. All fuels in the matrix were matched for total released energy and combustion phasing, using a cetane improving additive. The changes in emission have been quantified with agreement between the relative trends observed with the integrated SMPS volume concentrations and filter measurements. In order to evaluate changes among fuels and measurements taken with the SMPS, various fuels were subjected to physical and chemical characterization in order to determine morphological and compositional changes.

Reducing the Emission of Particles from a Diesel Engine by Adding an Oxygenate to the Fuel

“…It can easily be seen that the addition of acetal influences the particle size throughout all measured particle sizes; however, the influence seems to be somewhat higher on larger particle sizes, i.e., particles with a mobility diameter of >130 nm. This effect on particle size when using oxygenated fuels has also been observed by other researchers (16).…”

“…Different organic compounds (for example, alcohols, ethers, and esthers) have been studied as potential additives to diesel, and the influence of the levels of particles as well as other components have been reported (3,(7)(8)(9)(10)(11)(12)(13). A general finding is that the reduction of particles seems to be linearly dependent on the oxygen content, and, thus, the blend with the highest oxygen content results in the highest reduction of particles (14)(15)(16). Most of the investigations also report that the effect of the chemical structure is negligible, compared to the effect of the oxygen content (14)(15)(16)(17).…”

“…A general finding is that the reduction of particles seems to be linearly dependent on the oxygen content, and, thus, the blend with the highest oxygen content results in the highest reduction of particles (14)(15)(16). Most of the investigations also report that the effect of the chemical structure is negligible, compared to the effect of the oxygen content (14)(15)(16)(17). Cheng et al, for example, formulated fuels blends with up to 15 wt % of oxygen and tested them in a Cummins B 5.9 directinjection diesel engine (14).…”

Ultra-Clean Fischer-Tropsch Fuels Production and Demonstration Project

“…For a detailed description of the Scanning Mobility Particle Sizer (SMPS) system, see Hallgren [14]. Backgrounds scan with and without the HEPA filter installed upstream of the dilution tunnel is found in Figure 5.6 showing the effectiveness of the HEPA filter.…”

A study on the control of NOx and particulate matter emissions from dimethyl ether combustion in compression ignition engines

“…Absence of carbon-carbon bond in its chemical structure helps to reduce soot emissions during combustion, but the same affects lubrication property of the fuel leading to wear and tear of moving parts that comes in contact with the fuel [29,193,194]. Oxygen rich fuel property of DME also helps to reduce PM as the absence of C-C bond inhibits the formation of PM and cause high oxidation of particulates [195][196][197]. The low viscosity and density of DME possess fuel handling issues.…”