This work presents a detailed analysis of the production design and economics of the cellulosic isobutanol conversion processes and compares cellulosic isobutanol with cellulosic ethanol and n-butanol in the areas of fuel properties and engine compatibility, fermentation technology, product purifi cation process design and energy consumption, overall process economics, and life cycle assessment. Techno-economic analysis is used to understand the current stage of isobutanol process development and the impact of key parameters on the overall process economics in a consistent way (i.e. using the same fi nancial assumptions, plant scale, and cost basis). The calculated minimum isobutanol selling price is $3.62/gasoline gallon equivalent ($/GGE) -similar to $3.66/GGE from the n-butanol process and higher than $3.26/GGE from the cellulosic ethanol conversion process. At the conversion stage, the n-butanol process emits the most direct CO 2 , at 26.42 kg CO 2 /GGE. Isobutanol and ethanol plants have relatively similar CO 2 emissions, at 21.91 kg CO 2 /GGE and 21.01 kg CO 2 /GGE, respectively. The consumptive water use of the biorefi neries increases in the following order: ethanol (8.19 gal/ GGE) < isobutanol (8.98 gal/GGE) < n-butanol (10.84 gal/GGE). Field-to-wheel life cycle greenhouse gas (GHG) emissions for the ethanol and n-butanol conversion processes are similar at 4.3 and 4.5 kg CO 2 -eq/GGE, respectively. The life cycle GHG emissions result for the isobutanol conversion process is 5.0 kg CO 2 -eq/GGE, approximately 17% higher than that of ethanol. The life cycle fossil fuel consumption is 39 MJ/GGE for n-butanol, 43 MJ/GGE for ethanol and 51 MJ/GGE for isobutanol. The energy return on investment for each biofuel is also determined and compared: isobutanol (2.2:1) < ethanol (2.7:1) < n-butanol (2.8:1).

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A single-cylinder, wall-guided, spark ignition direct injection engine was used to study the impact of engine operating parameters on engine-out particle number (PN) emissions. Experiments were conducted with certification gasoline and a splash blend of 20% fuel grade ethanol in gasoline (E20), at four steady-state engine operating conditions. Independent engine control parameter sweeps were conducted including start of injection, injection pressure, spark timing, exhaust cam phasing, intake cam phasing, and air−fuel ratio. The results show that fuel injection timing is the dominant factor impacting PN emissions from this wall-guided gasoline direct injection engine. The major factor causing high PN emissions is fuel liquid impingement on the piston bowl. By avoiding fuel impingement, more than an order of magnitude reduction in PN emission was observed. Increasing fuel injection pressure reduces PN emissions because of smaller fuel droplet size and faster fuel−air mixing. PN emissions are insensitive to cam phasing and spark timing, especially at high engine load. Cold engine conditions produce higher PN emissions than hot engine conditions due to slower fuel vaporization and thus less fuel−air homogeneity during the combustion process. E20 produces lower PN emissions at low and medium loads if fuel liquid impingement on piston bowl is avoided. At high load or if there is fuel liquid impingement on piston bowl and/or cylinder wall, E20 tends to produce higher PN emissions. This is probably a function of the higher heat of vaporization of ethanol, which slows the vaporization of other fuel components from surfaces and may create local fuel-rich combustion or even pool-fires.

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The negative temperature coefficient (NTC) region of alkane autoignition was observed for the first time in the Ignition Quality Tester (IQT). The C 7 isomers studied included n-heptane, 3-ethylpentane, 2,4-dimethylpentane, 2,3dimethylpentane, and 2,2,3-trimethylbutane. The temperatures of the fuel−air mixture ranged from 650 to 1023 K with pressures of 0.5, 1.0, and 1.5 MPa at equivalence ratios between 0.8 and 1.0. The longer autoignition times of increasingly branched isomers allowed the reacting mixtures sufficient time to reach a pseudohomogeneous state, so that the kinetic behavior was similar to that observed in homogeneous rapid compression machine (RCM) and shock tube experiments. Although the IQT produced longer ignition delays than RCM data, the order of ignition delays for the various isomers was the same; that is, isomers with more branching had reduced reactivity and the location of the methyl group among equally branched isomers also affected reactivity. The characteristic NTC region was observed from all of the fuels at 0.5 MPa, except for n-heptane which had ignition delays too short to overcome the effects of fuel−air heterogeneity on autoignition. However, reducing the pressure to 0.2 MPa further increased the ignition delay so that NTC behavior was observed for n-heptane. A computational fluid dynamics model was used to study fuel evaporation and fuel−air mixing, and a 0-D homogeneous batch reactor was used to model the ignition of the C 7 isomers. The latter produced reasonable levels of agreement with experiments across the temperature range. The 0-D chemical kinetic model also successfully modeled hexadecane autoignition in the IQT at long ignition delays (>20 ms). However, coupled computational fluid dynamics/kinetic model may be required at short ignition delays (<20 ms), because the ignition process is affected by spray dynamics and mixture heterogeneity effects. NTC behavior for the low-volatility fuel 2,2,4,4,6,8,8heptamethylnonane (isocetane) was also measured experimentally for the first time. These results suggest that IQT ignition delay measurements at conditions (pressure and temperature) producing sufficiently long times (>20 ms) have the potential to provide meaningful data to assist in the validation of combustion kinetic mechanisms.

Development of advanced compression ignition and low-temperature combustion engines is increasingly dependent on chemical kinetic ignition models. However, rigorous experimental validation of kinetic models has been limited under engine-like conditions. For example, shock tubes and rapid compression machines are usually restricted to premixed gas-phase studies, precluding the study of heterogeneous combustion and the use of low-volatility surrogates for commercial diesel fuels. The Ignition Quality Tester (IQT) is a constant-volume spray combustion system designed to measure ignition delay of low-volatility fuels, having the potential to validate ignition models. However, a better understanding of the IQT's fuel spray and combustion processes is necessary to enable chemical kinetic studies. As a first step, n-heptane was studied because numerous reduced chemical mechanisms are available in the literature as it is a common diesel fuel surrogate, as well as a calibration fuel for the IQT. A modified version of the KIVA-3V software was utilized to develop a three-dimensional computational fluid dynamics (CFD) model that accurately and efficiently reproduces n-heptane ignition behavior and temporally resolves temperature and equivalence ratio regions inside the IQT. Measured fuel spray characteristics (e.g., spray-tip velocity, spray cone-angle, and flow oscillation) for n-heptane were programmed into the CFD model. Sensitivity analyses of fuel droplet size and velocity showed that their effects on ignition delay were small compared to the large chemical effects of increased chain branching in the isomers 2-methylhexane and 2,4dimethylpentane. CFD model predictions of ignition delay using reduced/skeletal chemical mechanisms for n-heptane (60-, 42-, and 33-species, and one-step chemistry) were compared, again indicating that chemical kinetics control the ignition process.

A free-piston rapid-compression facility (RCF) has been developed at the University of Michigan (UM) for use in studying high-temperature combustion phenomena, including gasphase combustion synthesis and homogeneous charge compression ignition systems. The facility is designed to rapidly compress a mixture of test gases in a nearly adiabatic process. A range of compression ratios, currently 16 to 37, can be obtained. The high temperatures and pressures generated by the RCF can be maintained for in excess of 50 ms, providing an order of magnitude increase in observation time over what can be obtained using shock tubes. The facility is instrumented for temperature and pressure measurements as well as optical access for use with laser and other optical diagnostics. This work describes the UM-RCF and its operation, establishes obtainable pressures and temperatures (over 1900 kPa and 970 K for predominately N 2 gas mixtures, and over 785 kPa and 2000 K for Ar gas mixtures), and demonstrates the repeatability of the UM-RCF experiments (< 3% run-to-run variability in peak pressure) for combustion studies. The experimental results for time histories of temperature and pressure are interpreted using analytical isentropic models. Comparison between the isentropic predictions and the experimental data indicate excellent agreement and support the conclusion that the core region of the test gases is nominally uniform and is compressed isentropically.2