Search Results

Work was performed to determine the feasibility of operating heavy-duty natural gas engines over a wide range of fuel compositions by evaluating engine performance and emission levels. Heavy-duty compressed natural gas engines from various engine manufacturers, spanning a range of model years and technologies, were evaluated using a diversity of fuel blends. Performance and regulated emission levels from these engines were evaluated using natural gas fuel blends with varying methane number (MN) and Wobbe Index in a dynamometer test cell. Eight natural gas blends were tested with each engine, and ranged from MN 75 to MN 100. Test engines included a 2007 model year Cummins ISL G, a 2006 model year Cummins C Gas Plus, a 2005 model year John Deere 6081H, a 1998 model year Cummins C Gas, and a 1999 model year Detroit Diesel Series 50G TK. All engines used lean-burn technology, except for the ISL G, which was a stoichiometric engine.

Greenhouse gas (GHG) emission targets are becoming more stringent for both automakers and electricity generators. With the introduction of plug-in hybrid and electric vehicles, transportation and electricity generation sectors become connected. This provides an opportunity for both sectors to work together to achieve the cost efficient reduction of CO2 emission. In addition, the abundant natural gas (NG) in USA is drawing increased attention from both policy makers and various industries due to its low cost and low carbon content. NG has the potential to ease the pressure from CO2 emission constraints for both the light duty vehicle (LDV) and the electricity generation sectors while simultaneously reducing their fuel costs. To quantify the benefit of this collaboration, an analytical model is developed to evaluate the total societal cost and CO2 emission for both sectors.

Interest in natural gas as an alternative fuel source to petroleum fuels for light-duty vehicle applications has increased due to its domestic availability and stable price compared to gasoline. With its higher hydrogen-to-carbon ratio, natural gas has the potential to reduce engine out carbon dioxide emissions, which has shown to be a strong greenhouse gas contributor. For part-load conditions, the lower flame speeds of natural gas can lead to an increased duration in the inflammation process with traditional port-injection. Direct-injection of natural gas can increase in-cylinder turbulence and has the potential to reduce problems typically associated with port-injection of natural gas, such as lower flame speeds and poor dilution tolerance. A study was designed and executed to investigate the effects of direct-injection of natural gas at part-load conditions.

Past experimental studies conducted by the current authors on a 13 liter 16.7:1 compression ratio heavy-duty diesel engine have shown that diesel-Compressed Natural Gas (CNG) Reactivity Controlled Compression Ignition (RCCI) combustion targeting low NOx emissions becomes progressively difficult to control as the engine load is increased. This is mainly due to difficulty in controlling reactivity levels at higher loads. For the current study, CFD investigations were conducted in CONVERGE using the SAGE combustion solver with the application of the Rahimi mechanism. Studies were conducted at a load of 5 bar BMEP to validate the simulation results against RCCI experimental data. In the low load study, it was found that the Rahimi mechanism was not able to predict the RCCI combustion behavior for diesel injection timings advanced beyond 30 degCA bTDC. This poor prediction was found at multiple engine speed and load points.

The compression ratio is a strong lever to increase the efficiency of an internal combustion engine. However, among others, it is limited by the knock resistance of the fuel used. Natural gas shows a higher knock resistance compared to gasoline, which makes it very attractive for use in internal combustion engines. The current paper describes the knock behavior of two gasoline fuels, and specific incylinder blend ratios with one of the gasoline fuels and natural gas. The engine used for these investigations is a single cylinder research engine for light duty application which is equipped with two separate fuel systems. Both fuels can be used simultaneously which allows for gasoline to be injected into the intake port and natural gas to be injected directly into the cylinder to overcome the power density loss usually connected with port fuel injection of natural gas.

Accounting for more than 90% of the molecules and more than 75% of the mass [1], hydrogen is the most abundant element in the universe. Due to the small molecule size and high buoyancy, it is not available in it’s free form on Earth. In recent years, hydrogen has gained the attention of the automotive industry [2–12] as an environmentally friendly alternative fuel. As a fuel, hydrogen is unique - it is odorless, colorless, tasteless, and burns invisibly in sunlight. Detection solutions such as the odorants used in natural gas are not yet feasible for automotive hydrogen because the available additives can poison the fuel cell catalyst. Additionally, the lower flammability limit of hydrogen is lower, and the flammability range wider, than fuels such as gasoline [13]. Hydrogen detection and its concentration measurement is usually done using hydrogen concentration sensors [13].

Impending emissions regulations for diesel engines, specifically exhaust particulate emissions have caused engine manufacturers to once again examine the potential of alternative fuels. Much interest has centered around compressed natural gas (CNG) due to its potential for low particulate and NOx emissions. Natural gas engine development projects have tended toward the use of current gasoline engine technology (stoichiometric mixtures, closed-loop fuel control, exhaust catalysts) or have applied the results of previous research in lean-burn gasoline engines (high-turbulence combustion chambers). These technologies may be inappropriate for foreseeable emissions targets in heavy-duty natural gas engines.

Dimethyl ether (DME) is an alternative to diesel fuel for use in compression-ignition engines with modified fuel systems and offers potential advantages of efficiency improvements and emission reductions. DME can be produced from natural gas (NG) or from renewable feedstocks such as landfill gas (LFG) or renewable natural gas from manure waste streams (MANR) or any other biomass. This study investigates the well-to-wheels (WTW) energy use and emissions of five DME production pathways as compared with those of petroleum gasoline and diesel using the Greenhouse gases, Regulated Emissions, and Energy use in Transportation (GREET®) model developed at Argonne National Laboratory (ANL).

Interest in natural gas as a fuel for light-duty transportation has increased due to its domestic availability and lower cost relative to gasoline. Natural gas, comprised mainly of methane, has a higher knock resistance than gasoline making it advantageous for high load operation. However, the lower flame speeds of natural gas can cause ignitability issues at part-load operation leading to an increase in the initial flame development process. While port-fuel injection of natural gas can lead to a loss in power density due to the displacement of intake air, injecting natural gas directly into the cylinder can reduce such losses. A study was designed and performed to evaluate the potential of natural gas for use as a light-duty fuel. Steady-state baseline tests were performed on a single-cylinder research engine equipped for port-fuel injection of gasoline and natural gas, as well as centrally mounted direct injection of natural gas.

An experimental program to develop a practical natural gas-fueled locomotive engine was conducted. Six natural gas-fueled combustion systems for an EMD 710-type locomotive engine were developed and tested. The six systems were evaluated in terms of NOx and CO emissions, thermal efficiency, knock tolerance, and other practical considerations. Each combustion system was tested at Notch 5, 100-percent load, Notch 8, 80-percent load, and Notch 8, 100-percent load conditions. In general, all of the technologies produced significantly lower NOx emissions than the baseline diesel engine. Based on the results of the tests and other analyses, a late cycle, high-injection pressure (LaCHIP) combustion system, using a diesel pilot-ignited, late cycle injection of natural gas with a Diesel-type combustion process, was determined to provide the most practical combustion system for a natural gas-fueled, EMD 710-powered locomotive.

The goal of this project was to demonstrate a low emissions, high efficiency heavy-duty on-highway natural gas engine. The emissions targets for this project are to demonstrate US 2010 emissions standards on the 13-mode steady state test. To meet this goal, a chemically correct combustion (stoichiometric) natural gas engine with exhaust gas recirculation (EGR) and a three way catalyst (TWC) was developed. In addition, a Sturman Industries, Inc. camless Hydraulic Valve Actuation (HVA) system was used to improve efficiency. A Volvo 11 liter diesel engine was converted to operate as a stoichiometric natural gas engine. Operating a natural gas engine with stoichiometric combustion allows for the effective use of a TWC, which can simultaneously oxidize hydrocarbons and carbon monoxide and reduce NOx. High conversion efficiencies are possible through proper control of air-fuel ratio.

A zero-dimensional cycle simulation model coupled with a chemical equilibrium model and a two-zone combustion model has been extended to predict nitric oxide formation and emissions from spark-ignited, lean-burn natural gas engines. It is demonstrated that using the extended Zeldovich mechanism alone, the NOx emissions from an 8.1-liter, 6-cylinder, natural gas engine were significantly under predicted. However, by combining the predicted NOx formation from both the extended Zeldovich thermal NO and the Fenimore prompt NO mechanisms, the NOx emissions were predicted with fair accuracy over a range of engine powers and lean-burn equivalence ratios. The effect of injection timing on NOx emissions was under predicted. Humidity effects on NOx formation were slightly under predicted in another engine, a 6.8-liter, 6-cylinder, natural gas engine. Engine power was well predicted in both engines, which is a prerequisite to accurate NOx predictions.

Small (up to 1% by volume) amounts of hydrogen (H2) were added to the intake charge of a single-cylinder, stoichiometric spark ignited engine to determine the effect of H2 addition on EGR tolerance. Two types of tests were performed at 1500 rpm, two loads (3.1 bar and 5.5 bar IMEP), two compression ratios (11:1 and 14:1) and with two fuels (gasoline and natural gas). The first test involved holding EGR level constant and increasing the H2 concentration. The EGR level of the engine was increased until the CoV of IMEP was > 5% and then small amounts of hydrogen were added until the total was 1% by volume. The effect of increasing the amount of H2 on engine stability was measured along with combustion parameters and engine emissions. The results showed that only a very small amount of H2 was necessary to stabilize the engine. At amounts past that level, increasing the level of H2 had no or only a very small effect.

An electromagnetic valve actuation (EVA) system was developed and applied to a Kohler Command Series engine. Engine development and testing was conducted for the purpose of evaluating the performance of the EVA-equipped engine, running on natural gas, in an engine-test laboratory environment. As part of this effort, a personal computer-based engine control system, which managed the fueling, ignition, throttling, and intake/exhaust valve control functions, was developed. The evaluation included an investigation into increasing engine power output and full load efficiency, as well as increased part load efficiency. Techniques including optimized valve events as a function of operating condition, and throttleless operation using early and late intake valve closing are presented. Engine simulation results are compared with actual engine data and presented in this paper.

CAI combustion has the potential to be the most clean combustion technology in internal combustion engines and is being intensively researched. Following the previous research on CAI combustion of gasoline fuel, systematic investigation is being carried out on the application of bio-fuels in CAI combustion. As part of an on-going research project, CAI combustion of methanol and ethanol was studied on a single-cylinder direct gasoline engine with an air-assisted injector. The CAI combustion was achieved by trapping part of burnt gas within the cylinder through using short-duration camshafts and early closure of the exhaust valves. During the experiment the engine speed was varied from 1200rpm to 2100rpm and the air/fuel ratio was altered from the stoichiometry to the misfire limit. Their combustion characteristics were obtained by analysing cylinder pressure trace.

This paper describes the use of an interactive NVH simulator in simulating and designing the sound character of a vehicle with a multi-mode engine and active exhaust valve. When designing a vehicle for sound quality, it is not sufficient to merely record some discreet operating conditions and modify these in a traditional sound quality program. The ability to simulate the sound quality of the vehicle over the full operating envelope is a necessity. Additionally, the ability to break down the sound contributions from intake, exhaust and other key contributors to the driver's ear, and manipulate these independently is also essential. In the case described here, an additional factor makes it mandatory that an accurate vehicle sound simulation is performed. The state of the engine and exhaust contribution, and thus the sound of the vehicle, change based on several parameters - vehicle speed, load demand and gear.

In recent years, HCCI (Homogeneous Charge Compression Ignition) combustion concept has attracted attention due to its potential for high fuel efficiency and low emissions. The essence of HCCI combustion is auto ignition of a very lean, homogeneous air-fuel mixture. However it leads to a major challenge for control engineers – controlling combustion timing to achieve required torque and optimal fuel consumption. There is a need for a simplified HCCI engine model to guide control strategy development. This paper presents such a control oriented model for a “heated intake air” HCCI engine concept that uses two streams of air (cold and hot) to achieve a variable temperature at intake valve closing.

Dual fuel (CI) engines provide an excellent means of maintaining high thermal efficiency and power while reducing emissions, particularly in situations where the primary fuel does not exhibit good auto-ignition characteristics. This is especially true of diesel engines operating on natural gas; usually in stationary applications such as distributed power generation. However, because two fuels are needed, the reliability of the engine is compromised. Therefore, this paper describes the first phase of a project that is to eventually manufacture dimethyl ether (DME) from natural gas and supply it to the pilot injector of a dual fuel engine. A chemical pilot plant has been built and operated, demonstrating an intermediate step in the production of DME from natural gas. DME is manufactured from methanol for pilot injection into a dual fuel engine operating with natural gas as the main fuel.

Variable cam timing strategies which utilize retard of the intake and exhaust valve events at part load have been previously shown to provide improved fuel consumption and feedgas NOx. These benefits can be increased by enhancing the combustion system with variable charge motion. A variable event duration valvetrain was simulated on engine dynamometer by running a series of short duration/low lift intake valve events. The fuel consumption benefit for this simulated variable event valvetrain is compared to that of dual retard VCT with variable charge motion. An estimated upper limit for the fuel consumption improvement potential of variable valve timing is presented. This upper limit includes both pumping work reduction and indicated efficiency improvement with high levels of exhaust residual dilution. The measured benefits of dual retard VCT and of the variable event valvetrain are compared to the estimated upper limit.

A spontaneous Raman scattering diagnostic was used to measure the residual fraction in a single-cylinder, 4-valve optically accessible engine. The engine was operated at 1500 rpm on pre-vaporized iso-octane at several intake manifold pressures (50-90 kPa). Cam phasing was varied to determine the effect of intake valve timing and valve overlap on the residual mass fraction of the engine. A simple model based on the ideal Otto cycle and 1D gas flow through the exhaust valves was proposed to analyze the results of the Raman experiment. The model showed good agreement (R2=0.91) with the experimental results and demonstrated its potential for use as a method to estimate the residual fraction in an engine from available dynamometer data. The experimental results showed that the residual fraction was reduced at higher manifold pressures due to less backflow through the exhaust valves and varied with intake cam phasing.