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Higher compression ratio and turbocharging, with engine downsizing can enable significant gains in fuel economy but require engine operating conditions that cause engine knock under high load. Engine knock can be avoided by supplying higher-octane fuel under such high load conditions. This study builds on previous MIT papers investigating Octane-On-Demand (OOD) to enable a higher efficiency, higher-boost higher compression-ratio engine. The high-octane fuel for OOD can be obtained through On-Board-Separation (OBS) of alcohol blended gasoline. Fuel from the primary fuel tank filled with commercially available gasoline that contains 10% by volume ethanol (E10) is separated by an organic membrane pervaporation process that produces a 30 to 90% ethanol fuel blend for use when high octane is needed. In addition to previous work, this paper combines modeling of the OBS system with passenger car and medium-duty truck fuel consumption and octane requirements for various driving cycles.

This paper explores the benefits that would be achieved if gasoline marketers produced and offered a higher-octane gasoline to the U.S. consumer market as the standard grade. By raising octane, engine knock constraints are reduced, so that new spark-ignition engines can be designed with higher compression ratios and boost levels. Consequently, engine and vehicle efficiencies are improved thus reducing fuel consumption and greenhouse gas (GHG) emissions for the light-duty vehicle (LDV) fleet over time. The main objective of this paper is to quantify the reduction in fuel consumption and GHG emissions that would result for a given increase in octane number if new vehicles designed to use this higher-octane gasoline are deployed. GT-Power simulations and a literature review are used to determine the relative brake efficiency gain that is possible as compression ratio is increased.

An experimental study was performed in a firing SI engine at conditions representative of the warmup phase of operation in which liquid gasoline films were established at various locations in the combustion chamber and the resulting impact on hydrocarbon emissions was assessed. Unique about this study was that it combined, in a firing engine environment, direct visual observation of the liquid fuel films, measurements of the temperatures these films were subjected to, and the determination from gas analyzers of burned and unburned fuel quantities exiting the combustion chamber - all with cycle-level resolution or better. A means of deducing the exhaust hydrocarbon emissions that were due to the liquid fuel films in the combustion chamber was developed. An increase in exhaust hydrocarbon emissions was always observed with liquid fuel films present in the combustion chamber.

Transport policy research seeks to predict and substantially reduce the future transport-related greenhouse gas emissions and fuel consumption to prevent negative climate change impacts and protect the environment. However, making such predictions is made difficult due to the uncertainties associated with the anticipated developments of the technology and fuel situation in road transportation, which determine the total fuel use and emissions of the future light-duty vehicle fleet. These include uncertainties in the performance of future vehicles, fuels' emissions, availability of alternative fuels, demand, as well as market deployment of new technologies and fuels. This paper develops a methodology that quantifies the impact of uncertainty on the U.S. transport-related fuel use and emissions by introducing a stochastic technology and fleet assessment model that takes detailed technological and demand inputs.

An experimental study was performed to develop a more fundamental understanding of the effects of secondary air injection (SAI) on exhaust gas emissions and catalyst light-off characteristics during cold start of a modern SI engine. The effects of engine operating parameters and various secondary air injection strategies such as spark retardation, fuel enrichment, secondary air injection location and air flow rate were investigated to understand the mixing, heat loss, and thermal and catalytic oxidation processes associated with SAI. Time-resolved HC, CO and CO₂ concentrations were tracked from the cylinder exit to the catalytic converter outlet and converted to time-resolved mass emissions by applying an instantaneous exhaust mass flow rate model. A phenomenological model of exhaust heat transfer combined with the gas composition analysis was also developed to define the thermal and chemical energy state of the exhaust gas with SAI.

This vehicle simulation study estimates the fuel economy benefits of an HCCI engine system and assesses the NOx, HC and CO aftertreatment performance required for compliance with emissions regulations on U.S. and European regulatory driving cycles. The four driving cycles considered are the New European Driving Cycle, EPA City Driving Cycle, EPA Highway Driving Cycle, and US06 Driving Cycle. For each driving cycle, the following influences on vehicle fuel economy were examined: power-to-weight ratio, HCCI combustion mode operating range, driving cycle characteristics, requirements for transitions out of HCCI mode when engine speeds and loads are within the HCCI operating range, fuel consumption and emissions penalties for transitions into and out of HCCI mode, aftertreatment system performance and tailpipe emissions regulations.

This paper evaluates how the fuel consumption of the average new U.S. passenger car will be penalized if engine and vehicle improvements continue to be focused on developing bigger, heavier and more powerful automobiles. We quantify a parameter called the Emphasis on Reducing Fuel Consumption (ERFC) and find that there has been little focus on improving fuel consumption in the U.S. over the past twenty years. In contrast, Europe has seen significantly higher ERFC. By raising the ERFC over the next few decades, we can reduce the average U.S. new car's fuel consumption by up to some 40 percent and cut the light-duty vehicle fleet's fuel use by about a quarter. Achieving substantial fuel use reduction will remain a major challenge if automobile size, weight and power continue to dominate.

This paper assesses the potential improvement of automotive powertrain technologies 25 years into the future. The powertrain types assessed include naturally-aspirated gasoline engines, turbocharged gasoline engines, diesel engines, gasoline-electric hybrids, and various advanced transmissions. Advancements in aerodynamics, vehicle weight reduction and tire rolling friction are also taken into account. The objective of the comparison is the potential of anticipated improvements in these powertrain technologies for reducing petroleum consumption and greenhouse gas emissions at the same level of performance as current vehicles in the U.S.A. The fuel consumption and performance of future vehicles was estimated using a combination of scaling laws and detailed vehicle simulations. The results indicate that there is significant potential for reduction of fuel consumption for all the powertrains examined.

An experimental study was performed to investigate the effects of various intake charge motion control valves (CMCVs) on mixture preparation, combustion, and hydrocarbon (HC) emissions during the cold start-up process of a port fuel injected spark ignition (SI) engine. Different charge motions were produced by three differently shaped plates in the CMCV device, each of which blocked off 75% of the engine's intake ports. Time-resolved HC, CO and CO2 concentrations were measured at the exhaust port exit in order to achieve cycle-by-cycle engine-out HC mass and in-cylinder air/fuel ratio. Combustion characteristics were examined through a thermodynamic burn rate analysis. Cold-fluid steady state experiments were carried out with the CMCV open and closed. Enhanced charge motion with the CMCV closed was found to shorten the combustion duration, which caused the location of 50% mass fraction burned (MFB) to occur up to 5° CA earlier for the same spark timing.

This paper explores the modeling of a lean boosted engine concept. Modeling provides a useful tool for investigating different parameters and comparing resultant emissions and fuel economy performance. An existing architectural concept has been tailored to a boosted hydrogen-enhanced lean-burn SI engine. The simulation consists of a set of Matlab models, part physical and part empirical, which has been developed to simulate a working engine. The model was calibrated with production engine data and experimental data taken at MIT. Combustion and emissions data come from a single cylinder research engine and include changes in air/fuel ratio, load and speed, and different fractions of the gasoline fuel reformed to H2 and CO. The outputs of the model are brake specific NOx emissions and brake specific fuel consumption maps along with cumulative NOx emissions and fuel economy for urban and highway drive cycles.

An experimental study was carried out that qualitatively examined the mixture preparation process in port fuel injected engines. The primary variables in this study were intake valve lift, intake valve timing, injector spray quality, and injection timing. A special visualization engine was used to obtain high-speed videos of the fuel-air mixture flowing through the intake valve, as well as the wetting of the intake valve and head in the combustion chamber. Additionally, videos were taken from within the intake port using a borescope to examine liquid fuel distribution in the port. Finally, a simulation study was carried out in order to understand how the various combinations of intake valve lifts and timings affect the flow velocity through the intake valve gap to aid in the interpretation of the videos.

Dilute operation of a SI engine offers attractive performance incentives. Lowered combustion temperatures and changes in the mixture composition inhibit NOx formation and increase the effective value of the ratio of burned gas specific heats, increasing gross indicated efficiency. Additionally, reduced intake manifold throttling minimizes pumping losses, leading to higher net indicated efficiency. These benefits are offset by the reduced combustion speed of dilute fuel-air mixtures, which can lead to high cycle-to-cycle variation and unacceptable engine behavior characteristics. Hydrogen enhancement can suppress the undesirable consequences of dilute operation by accelerating the combustion process, thereby extending the dilution limit. Hydrogen would be produced on-board the vehicle with a gasoline reforming device such as the plasmatron. High dilution at higher loads would necessitate boosting to meet the appropriate engine specific power requirements.

A study at MIT of the energy consumption and greenhouse gas emissions from advanced technology future automobiles has compared fuel cell powered vehicles with equivalent gasoline and diesel internal combustion engine (ICE) powered vehicles [1][2]. Current data regarding IC engine and fuel cell vehicle performance were extrapolated to 2020 to provide optimistic but plausible forecasts of how these technologies might compare. The energy consumed by the vehicle and its corresponding CO2 emissions, the fuel production and distribution energy and CO2 emissions, and the vehicle manufacturing process requirements were all evaluated and combined to give a well-to-wheels coupled with a cradle-to-grave assessment. The assessment results show that significant opportunities are available for improving the efficiency of mainstream gasoline and diesel engines and transmissions, and reducing vehicle resistances.

Experiments were performed to identify the knock trends of lean hydrocarbon-air mixtures, and such mixtures enhanced with hydrogen (H2) and carbon monoxide (CO). These enhanced mixtures simulated 15% and 30% of the engine's gasoline being reformed in a plasmatron fuel reformer [1]. Knock trends were determined by measuring the octane number (ON) of the primary reference fuel (mixture of isooctane and n-heptane) supplied to the engine that just produced audible knock. Experimental results show that leaner operation does not decrease the knock tendency of an engine under conditions where a fixed output torque is maintained; rather it slightly increases the octane requirement. The knock tendency does decrease with lean operation when the intake pressure is held constant, but engine torque is then reduced.

Experiments were conducted to determine the effects of substantial spark retard on combustion, hydrocarbon (HC) emissions, and exhaust temperature, under cold engine conditions. A single-cylinder research engine was operated at 20° C fluid temperatures for various spark timings and relative air/fuel ratios. Combustion stability was observed to decrease as the phasing of the 50% mass fraction burned (MFB) occurred later in the expansion stroke. A thermodynamic burn rate analysis indicated combustion was complete at exhaust valve opening with -20° before top dead center (BTDC) spark timings. Chemical and thermal energy of the exhaust gas was tracked from cylinder-exit to the exhaust runner. Time-resolved HC concentrations measured in the port and runner were mass weighted to obtain an exhaust HC mass flow rate. Results were compared to time averaged well downstream HC levels.

When hydrogen is added to a gasoline fueled spark ignition engine the lean limit of the engine can be extended. Lean running engines are inherently more efficient and have the potential for significantly lower NOx emissions. In the engine concept examined here, supplemental hydrogen is generated on-board the vehicle by diverting a fraction of the gasoline to a plasmatron where a partial oxidation reaction is initiated with an electrical discharge, producing a plasmatron gas containing primarily hydrogen, carbon monoxide, and nitrogen. Two different gas mixtures were used to simulate the plasmatron output. An ideal plasmatron gas (H2, CO, and N2) was used to represent the output of the theoretically best plasmatron. A typical plasmatron gas (H2, CO, N2, and CO2) was used to represent the current output of the plasmatron. A series of hydrogen addition experiments were also performed to quantify the impact of the non-hydrogen components in the plasmatron gas.

The purpose of this work was to develop an understanding of how liquid fuel transported into the cylinder of a port-fuel-injected gasoline-fueled SI engine contributes to hydrocarbon (HC) emissions. To simulate the liquid fuel flow from the valve seat region into the cylinder, a specially designed fuel probe was developed and used to inject controlled amounts of liquid fuel onto the port wall close to the valve seat. By operating the engine on pre-vaporized Indolene, and injecting a small amount of liquid fuel close to the valve seat while the intake valve was open, we examined the effects of liquid fuel entering the cylinder at different circumferential locations around the valve seat. Similar experiments were also carried out with closed valve injection of liquid fuel at the valve seat to assess the effects of residual blowback, and of evaporation from the intake valve and port surfaces.

Experiments to study the effects of oxygenated fuels on emissions and combustion were performed in a single-cylinder direct-injection (DI) diesel engine. A matrix of oxygen containing fuels assessed the impact of weight percent oxygen content, oxygenate chemical structure, and oxygenate volatility on emissions. Several oxygenated chemicals were blended with an ultra-low sulfur diesel fuel and evaluated at an equivalent energy release and combustion phasing. Additional experiments investigated the effectiveness of oxygenated fuels at a different engine load, a matched fuel/air equivalence ratio, and blended with a diesel fuel from the Fischer-Tropsch process. Interactions between emissions and critical engine operating parameters were also quantified. A scanning mobility particle sizer (SMPS) was used to evaluate particle size distributions, in addition to particulate matter (PM) filter and oxides of nitrogen (NOx) measurements.

The transportation sector in the United States is a major contributor to global energy consumption and carbon dioxide emission. To assess the future potentials of different technologies in addressing these two issues, we used a family of simulation programs to predict fuel consumption for passenger cars in 2020. The selected technology combinations that have good market potential and could be in mass production include: advanced gasoline and diesel internal combustion engine vehicles with automatically-shifting clutched transmissions, gasoline, diesel, and compressed natural gas hybrid electric vehicles with continuously variable transmissions, direct hydrogen, gasoline and methanol reformer fuel cell hybrid electric vehicles with direct ratio drive, and battery electric vehicle with direct ratio drive.

Modern natural gas-to-liquids (GTL) conversion processes (Fischer-Tropsch liquid fuels (FTL)) offers an attractive means for making synthetic liquid fuels. Military diesel and jet fuels are procured under Commercial Item Description (CID) A-A-52557 (based on ASTM D 975) and MIL-DTL-83133/MIL-DTL-5624 (JP-8/JP-5), respectively. The Single Fuel Forward (single fuel in the battlefield) policy requires the use of JP-8 or JP-5 (JP-8/5). Fuel properties crucial to fuel system/engine performance/operation are identified for both old and new tactical/non-tactical vehicles. The 21st Century Truck program is developing technology for improved safety, reduced harmful exhaust emissions, improved fuel efficiency, and reduced cost of ownership of future military and civilian ground vehicles (in the heavy duty category having gross vehicle weights exceeding 8500 pounds).[1]