Stuart R. Bell

Extension of the Lean Operating Limit for Natural Gas Fueling of a Spark Ignited Engine Using Hydrogen Blending

The performance, emissions and combustion characteristics of lean mixtures of natural gas and hydrogen were studied in a conventional spark ignited engine. Specifically, mixtures of natural gas blended with 5, 10 and 15 percent by volume hydrogen were considered. Engine performance parameters included power (BHP), thermal efficiency (BTE), specific fuel consumption (BSFC), coefficient of variation in mean effective pressure, cumulative energy release schedule, and emissions of CO, NO x and hydrocarbons. Major conclusions of the work include: (t) at equivalence ratios leaner than 0.80, improvements in BHP, BSFC, and BTE were significant wilh hydrogen addition; (ii) significant extension of the lean operating limit to lower equivalence ratios was demonstrated with increasing hydrogen concentrations in natural gas; (iii) emissions of CO, NO^ and hydrocarbons decreased as equivalence ratio was reduced until partial burning became predominant; (iv) hydrogen addition appeared to allow stable engine operation wi...

Performance and heat release analysis of a pilot-ignited natural gas engine

Abstract The influence of engine operating variables on the performance, emissions and heat release in a compression ignition engine operating in normal diesel and dual-fuel modes (with natural gas fuelling) was investigated. Substantial reductions in NOx emissions were obtained with dual-fuel engine operation. There was a corresponding increase in unburned hydrocarbon emissions as the substitution of natural gas was increased. Brake specific energy consumption decreased with natural gas substitution at high loads but increased at low loads. Experimental results at fixed pilot injection timing have also established the importance of intake manifold pressure and temperature in improving dual-fuel performance and emissions at part load.

An Investigation of Lean Combustion in a Natural Gas-Fueled Spark-Ignited Engine

Natural gas has been used extensively as an engine fuel in gas pipeline transmission applications and, more recently, as a fuel for transportation applications including both light-duty and heavy-duty vehicles. The objective of this work was to investigate the performance and emission characteristics of natural gas in an original equipment manufacturer (OEM), light-duty, spark-ignited engine being operated in the lean fueling regime and compare the operation with gasoline fueling cases. Data were acquired for several operating conditions of speed, throttle position, air-fuel equivalence ratio, and spark timing for both fuels. Results showed that for stoichiometric fueling, with a naturally aspirated engine, a power loss of 10 to 15 percent can be expected for natural gas over gasoline fueling. For lean operation, however, power increases can be expected for equivalence ratios below about Φ = 0.80 with natural gas fueling as compared to gasoline. Higher brake thermal efficiencies can also be expected with natural gas fueling with maximum brake torque (MBT) timings over the range of equivalence ratios investigated in this work. Coefficient of variation (COV) data based on the indicated mean effective pressure (IMEP) demonstrated that the engine is much less sensitive to equivalence ratio leaning for natural gas fueling as compared to gasoline cases. The lean limit for a COV of 10 percent was about Φ = 0.72 for gasoline and Φ = 0.63 for natural gas. Lean fueling resulted in significantly reduced NO x levels where a lower plateau for NO x concentrations was reached at Φ near or below 0. 70, which corresponded to about 220 ppm. For natural gas fueling, this corresponded to about 1.21 gm/(kW-h). Finally, with MBT timings, relatively short heat release durations were obtained for lean fueling with natural gas compared to gasoline.

Natural gas fueling of a caterpillar 3406 diesel engine

This paper reports on a Caterpillar 3406 turbocharged diesel engine which was converted to operate in a natural gas with diesel pilot ignition mode and was evaluated for performance and emission characteristics for both diesel and natural gas operation. Full-load power was achieved with natural gas fueling without knock. Similar fuel efficiencies were obtained with natural gas fueling at high loads, but efficiencies were lower for low loads. Bosch smoke numbers were reduced by over 50 percent with natural gas fueling for all cases investigated. NO[sub x] emissions were found to be lower at low loads and at high speeds under high load. CO emissions were significantly increased for natural gas fueling while CO[sub 2] concentrations in the exhaust were reduced for natural gas fueling.

Full-Fuel-Cycle Approach to Vehicle Emissions Modeling: A Case Study of Gasoline in the Southeastern Region of the United States

The use of full-fuel-cycle analysis as a scientific, economic, and policy tool for the evaluation of alternative sources of transportation energy has become increasingly widespread. However, consistent methods for performance of these types of analyses are only now becoming recognized and utilized. The work presented here provides a case study of full-fuel-cycle analysis methods applied to the evaluation of gasoline in the southeastern region of the United States. Results of the study demonstrate the significance of nonvehicle processes, such as fuel refining, in terms of energy expenditure and emissions production. Unique to this work is the application of the MOBILE5 mobile emissions model in the full-fuel-cycle analysis. Estimates of direct and indirect greenhouse gas production are also presented and discussed using the full-fuel-cycle analysis method.

Prediction of household levels of greenhouse-gas emissions from personal automotive transportation

The work presented in this paper demonstrates that different subgroups in the population described by various economic and demographic characteristics have different levels of greenhouse gas emissions from personal automotive transportation. Further these characteristics may be assigned a rank or importance in terms of association with emissions levels. And once socioeconomic characteristics of a household are known, emissions levels may be predicted.

Full-fuel-cycle modeling for alternative transportation fuels

Utilization of alternative fuels in the transportation sector has been identified as a potential method for mitigation of petroleum-based energy dependence and pollutant emissions from mobile sources. Traditionally, vehicle tailpipe emissions have served as sole data when evaluating environmental impact. However, considerable differences in extraction and processing requirements for alternative fuels makes evident the need to consider the complete fuel production and use cycle for each fuel scenario. The work presented here provides a case study applied to the southeastern region of the United States for conventional gasoline, reformulated gasoline, natural gas, and methanol vehicle fueling. Results of the study demonstrate the significance of the nonvehicle processes, such as fuel refining, in terms of energy expenditure and emissions production. Unique to this work is the application of the MOBILE5 mobile emissions model in the full-fuel-cycle analysis. Estimates of direct and indirect greenhouse gas production are also presented and discussed using the full-cycle-analysis method.

Use of an Electrically Heated Catalyst to Reduce Cold-Start Emissions in a Bi-Fuel Spark Ignited Engine

Reduction of cold-start emissions using electrically-heated catalyst (EHC) technology was the focus of this work. Comprehensive emission measurements of CO, CO 2 , NO x , and total hydrocarbons (THC) are reported for a spark-ignited engine operated on baseline gasoline and compressed natural gas (CNG). Electric heating times of 0, 20, and 40 S with and without secondary air injection were investigated. The 40-second electric catalyst heating with secondary air injection scenario yielded the greatest catalyst system (EHC + OEM three-way catalyst) conversion efficiencies for THC, CO, and NO x for gasoline and natural gas fueling. Electric catalyst heating coupled with secondary air injection significantly improved THC and CO emissions for gasoline fueling. THC oxidation was difficult for CNG fueling due to the high content of nonreactive methane in the fuel. The independence of NO x emissions on heating time was demonstrated for all fueling cases.

Parametric studies on a coal-fueled diesel engine

Abstract The ignition and combustion processes of coal-water slurry (CWS) in a prechamber type diesel engine were investigated in this work. Specific engine and fuel parameters studied included: (I) needle lift pressure; (ii) inlet air temperature; (iii) fuel injection timing; and (iv) percent coal loading in the slurry fuel. Analysis of the experimental data utilized a numerical simulation of the combustion process using submodels for the key physical and chemical processes. Energy release schedules were determined using a one-zone thermodynamic analysis with measured cylinder pressure as a function of time. Successful operation of the engine using the coal slurry required modifications to the engine and support systems. These modifications are briefly discussed in this paper. The major conclusions of the work include: (I) higher needle lift pressures led to shorter ignition delay times for the CWS fuel; (ii) increasing the inlet air temperature shortened ignition delay times and improved burning rates o...