Natural Gas Spark Ignition Engine Research Articles

Optimization of a natural gas SI engine employing EGR strategy using a two-zone combustion model

Natural gas has been recently used as an alternative to conventional fuels in order to satisfy some environmental and economical concerns. In this study, a natural gas spark-ignition engine employing cooled exhaust gas recirculation (EGR) strategy in a high pressure inlet condition was optimized. Both engine compression ratio and start of combustion timing were optimized in order to obtain the lowest fuel consumption accompanied with high power and low emissions. That was achieved numerically by developing a computer simulation of the four-stroke spark-ignition natural gas engine. A two-zone combustion model was developed to simulate the in-cylinder conditions during combustion. A kinetic model based on the extended Zeldovich mechanism was also developed in order to predict NO emission. In addition, a knocking model was incorporated with the two-zone combustion model in order to predict any auto-ignition that might occur. It was found that the value of the compression ratio at which the minimum fuel consumption occurs varies with the engine speed. A minimum fuel consumption of about 200g/kWh was achieved at an engine speed of 1500rpm, inlet conditions of 200kPa and 333K, and a compression ratio of about 12. Also, it was found that cooled EGR can significantly reduce NO emission at high compression ratio conditions. NO emission decreased by about 28% when EGR was increased from 20% at compression ratio of 10 to 27% at compression of 12 at the same engine speed of 3000rpm.

Experimental study on thermal efficiency and emission characteristics of a lean burn hydrogen enriched natural gas engine

In order to analyze the effect of hydrogen addition on natural gas (NG) engine's thermal efficiency and emission, an experimental research was conducted on a spark ignition NG engine using variable composition hydrogen/CNG mixtures (HCNG). The results showed that hydrogen enrichment could significantly extend the lean operation limit, improve the engine's lean burn ability, and decrease burn duration. However, nitrogen oxides ( NO x ) were found to increase with hydrogen addition if spark timing was not optimized according to hydrogen's high burn speed. Also found when spark timing was set at constant was that hydrogen addition actually increases heat transfer out of the cylinder due to smaller quenching distance and higher combustion temperature, thus is not good to improve thermal efficiency if combined with the effect of non-ideal spark timing. But if spark timing was retarded to MBT, taking advantage of hydrogen's high burn speed, NO x emissions exhibited no obvious increase after hydrogen addition and engine thermal efficiency increased with the increase of hydrogen fraction. Unburned hydrocarbon always decreased with the increase of hydrogen fraction.

Spark ignition natural gas engines—A review

Natural gas is a promising alternative fuel to meet strict engine emission regulations in many countries. Natural gas engines can operate at lean burn and stoichiometric conditions with different combustion and emission characteristics. In this paper, the operating envelope, fuel economy, emissions, cycle-to-cycle variations in indicated mean effective pressure and strategies to achieve stable combustion of lean burn natural gas engines are highlighted. Stoichiometric natural gas engines are briefly reviewed. To keep the output power and torque of natural gas engines comparable to those of their gasoline or Diesel counterparts, high boost pressure should be used. High activity catalyst for methane oxidation and lean deNOx system or three way catalyst with precise air–fuel ratio control strategies should be developed to meet future stringent emission standards. 2006 Elsevier Ltd. All rights reserved.

Evaluation of Emissions from New and In-Use Transit Buses in Mexico City, Mexico

The West Virginia University Transportable Heavy-Duty Emissions Testing Laboratory was used to evaluate exhaust emissions from nine transit buses from six separate manufacturers, as commissioned by the Mexico City, Mexico, Secretariat of the Environment. The vehicles included a hybrid-drive diesel bus, two buses with lean-burn spark-ignited compressed natural gas (CNG) engines, and six buses powered by conventional diesel engines. Vehicle testing weights (curb weight plus passenger weight) ranged from 26,996 lb (12,256 kg) to 57,025 lb (25,889 kg), and passenger capacities ranged from 85 to 161. Two driving cycles, the European Transient Cycle (ETC, also known as the FIGE transient cycle) and a new, three-mode Mexico City Schedule, were used to simulate in-use driving conditions during emissions measurements. Diesel fuels with three different sulfur concentrations (15, 150, and 350 ppm) were also examined, and the lowest-sulfur fuel (15 ppm) was not found to have an appreciable direct effect on emissions. When the ETC was used, oxides of nitrogen (NOx) emissions varied from 5.5 to 11.6 g/mi, whereas particulate matter emissions varied from 0.02 to 0.86 g/mi. Significant differences in emissions and fuel economy for the two CNG buses raised the issue that fuel delivery systems must be optimized for operation at high altitudes. The differences in fuel economy and NOx emissions from the hybrid bus for congested and noncongested driving conditions were significantly less than those from the conventional diesel and CNG buses.

Evaluation of Emissions from New and In-Use Transit Buses in Mexico City, Mexico

The West Virginia University Transportable Heavy-Duty Emissions Testing Laboratory was used to evaluate exhaust emissions from nine transit buses from six separate manufacturers, as commissioned by the Mexico City, Mexico, Secretariat of the Environment. The vehicles included a hybrid-drive diesel bus, two buses with lean-burn spark-ignited compressed natural gas (CNG) engines, and six buses powered by conventional diesel engines. Vehicle testing weights (curb weight plus passenger weight) ranged from 26,996 Ib (12,256 kg) to 57,025 Ib (25,889 kg), and passenger capacities ranged from 85 to 161. Two driving cycles, the European Transient Cycle (ETC, also known as the FIGE transient cycle) and a new, three-mode Mexico City Schedule, were used to simulate in-use driving conditions during emissions measurements. Diesel fuels with three different sulfur concentrations (15, 150, and 350 ppm) were also examined, and the lowest-sulfur fuel (15 ppm) was not found to have an appreciable direct effect on emissions....

Gross carbon emissions from alternative transport fuels in India

The objective of the paper is to present a life-cycle assessment of pollution from alternative transport fuels in Indian conditions. The present study is limited to gross carbon emission (as CO 2 ) because of its serious implications for global warming. Indicative values of gross carbon emissions from bioethanol, CNG and electrical energy sources have been evaluated from industrial data and compared with those from oil. The energy and environmental analyses of bioethanol production in India show that bioethanol can significantly reduce global CO 2 emissions and, if used as a petrol blend, can help reduce oil imports as well as aromatics pollution from unleaded petrol (now introduced into India). The method used in this research has two main components. The first is an examination of each energy industry in detail, using primary sources of data from power stations, oil refineries and anhydrous ethanol production from molasses. The processes involved in each case are examined, taking into account energy use in any necessary auxiliary activities to evaluate the total carbon emissions. The second component is a detailed examination of one specific form of public transport. This is a three-wheeled 8-seater used in the city of Lucknow in North India. It is chosen because it is available with a petrol or compressed natural gas (CNG) spark-ignition engine (and hence could alternatively be ethanol-fuelled) and in a battery-electric version. Both parts of this data-gathering have been specific to the situation in India. In energy conversion the refinery crude composition and processes, basic resources of biomass and the mix of primary energy for electricity generation are different in each country. The types of vehicle used also vary considerably from region to region. It is observed that while CNG and electric-powered vehicles may have low and zero tailpipe emissions respectively, gross pollution from such vehicles and their associated resource systems may be significant. In the case of electrically-propelled vehicles the gross carbon emission is comparable with that for similar petrol-engine vehicles since about 80% of electricity production in India is fossil-fuel-based. In comparison, CNG shows a reduction of about a third. Alcohol-fuelled vehicles, by comparison, can show neutral (i.e., zero net) carbon emission. The importance of gross pollution assessments in rational choice of a fuel cannot be overemphasised.

Comparative study of some experimental methods to characterize the combustion process in a SI engine

Seven common methods based on in-cylinder data, usually applied to determine the combustion parameters (ignition delay and combustion duration), are compared using in-cylinder data provided from a natural gas spark ignition engine operating under lean conditions. The influence of three engine operating parameters: spark advance, throttle opening and fuel/air equivalence ratio, on combustion parameters are tested using every method and the results are compared. The application of these methods on average and individual cycles is also performed. The advantages and disadvantages of these methods are presented and discussed. Some methods can be used only for the ignition delay determination. A comparison with a motor-cycle, so a specific experimental device, is necessary for three methods. Others are very sensitive to noise, or can be used only in some restricted area of engine operating conditions. One method needs calculations based on several experimental assumptions.

A comparison of the relative effects of fuel composition and ignition energy on the early stages of combustion in a natural gas spark ignition engine using simulation

Spark ignition engines operating on natural gas (NG) show advantages over petrol and diesel alternatives in terms of precatalyst emissions. However, such engines are affected much more than their petrol counterparts by the long combustion delay of the main fuel component, methane. The sensitivity of combustion delay to fuel/diluent chemistry means that this issue is exaggerated by the presence in the NG of variable concentrations of higher hydrocarbons and of inorganic components, arising from the worldwide variability of NG or from the use of exhaust gas recirculation. The present article reports on a study using a large-scale three-dimensional simulation, incorporating computational fluid dynamics (CFD) and fully detailed chemical kinetics, of the early stages of NG combustion in a spark ignition engine. The focus is on comparing the relative influences of gas composition (i.e. the ethane content of the NG, and carbon dioxide in the oxidant/diluent) with the effects of ignition source location and energy on the early progress of the combustion. The results of the studies show that, although the presence of ethane enhances the combustion propagation rate and reduces delay time, and carbon dioxide has the reverse effect, the influences of the characteristics (energy and location) of the ignition source dominate over quite large changes in mixture composition. These findings have practical ramifications for the development of strategies for reducing combustion delay time in NG-fuelled engines.

PARTICLE EMISSIONS FROM COMPRESSED NATURAL GAS ENGINES

This paper presents the results of measurements conducted to determine particle and gas emissions from two large compressed natural gas (CNG) spark ignition (SI) engines. Particle size distributions in the range from 0.01–30 μm, and gas composition were measured for five power settings of the engines: 35, 50, 65, 80 and 100% of full power. Particle emissions in the size range between 0.5 and 30 μm, measured by the aerodynamic particle sizer (APS), were very low at a level below two particles cm −3. These concentrations were comparable with average ambient concentration, and were not considered in the succeeding analysis. Both engines produce significant amounts of particles in the size range between 0.015 and 0.7 μm, measured by the scanning mobility particle sizer (SMPS). Maximum number of concentrations of about 1×10 7 particles cm −3 were very similar for both engines. The CMDs were in the range between 0.020 and 0.060 μm. The observed levels of particulate emission are in terms of number of the same order as emissions from heavy duty diesel engines (Morawska et al., Environ. Sci. Tech. 32, 2033–2042). On the other hand, emissions of CO and NO x of 5.53 and 3.33 g kW h −1, respectively, for one of the tested engines, were considerably lower than set by the standards. According to the specifications for the gas emissions, provided by the US EPA (US EPA, 1997), this engine can be considered as a “low-emission” engine, although emissions of submicrometer particles are of the same order as heavy-duty diesel vehicles.

In-Cylinder Combustion in a Spark-Ignited Natural Gas Engine. 2nd Report. Effect of Swirl Ratio, Spark Plug Electrode Direction and Spark Plug Position.

An experimental study was made to investigate the effect of swirl ratio, spark plug electrode direction and spark plug position on in-cylinder combustion in a spark-ignited natural gas engine. Flame propagation in a single-cylinder visualization engine was observed from bottom of the piston by the high speed schlieren method, over the wide range of nominal swirl ratio, spark plug electrode direction and spark plug position. The results showed that larger swirl ratio led to more rapid flame propagation, resulting in larger heat release rate and larger cylinder pressure. Spark plug electrode direction had little effect on flame propagation, resulting in little difference in heat release rate and cylinder pressure. Farther spark plug position to cylinder axis led to more rapid flame propagation, resulting in larger heat release rate and larger cylinder pressure, excluding extremely far spark plug position.

In-Cylinder Combustion in a Spark-Ignited Natural Gas Engine. 1st Report. Effect of Combustion Chamber Configuration and Top Clearance.

An experimental study was made to investigate the effect of combustion chamber configuration and top clearance on in-cylinder combustion in a spark-ignited natural gas engine. Flame propagation in a single-cylinder visualization engine was measured from the cylinder axis direction by the high speed schlieren method, over the wide range of combustion chamber configuration and top clearance. The results showed that smaller piston cavity diameter led to more rapid flame propagation, resulting in larger heat release rate and larger cylinder pressure. Top clearance had little effect on flame propagation, resulting in little difference in heat release rate and cylinder pressure.

火花点火式天然ガス機関の燃焼室内における燃焼特性および機関運転条件の影響

An experimental study was made to investigate in-cylinder combustion in a spark-ignited natural gas engine and its dependence on engine running conditions. Flame propagation in a single-cylinder visualization engine was measured from the cylinder axis direction by the high speed schlieren method, over the wide range of spark timing and excess air ratio. The results showed that flame did not propagate concentrically around spark plug electrode, but was shifted by swirl flow. The gravity center of flame area moves corresponding to flow field in the combustion chamber. In the case of partial-burning, flame left from the spark plug electrode, resulting in no more propagation. Cylinder pressure increase is delayed compared to flame propagation. Heat release is detected when flame area occupies around 4% of the combustion chamber area. Heat release shows its maximum when flame area occupies around 70% of the combustion chamber area. Flame area varies cycle-to-cycle within ±10% to its average, which is smaller than cycle variation of swirl velocity. Spark timing had little effect on flame propagation and its speed. Larger excess air ratio resulted in more slender flame, slower and more shifted flame propagation. Flame propagation speed, which is negatively proportional to excess air ratio, gets half from about 10m/s to about 5m/s as excess air ratio changes from 1.3 to 1.6.

火花点火式天然ガス機関の燃焼室内における流動特性に及ぼす機関諸元の影響

An experimental study was made to investigate the effects of engine specifications on in-cylinder flow field in a spark-ignited natural gas engine. The instantaneous two-dimentional flow field in a single-cylinder visualization engine was measured by using the PTV method over the wide range of piston combustion chamber configuration, top clearance, and nominal swirl ratio. The results showed that swirl is more shifted to the outward radial direction in expansion stroke as piston cavity diameter decreases. In compression stroke, however, the extent of swirl shift is almost constant even if piston cavity diameter varies. Reverse squish is more accelerated than swirl as piston cavity diameter decreases. Smaller piston cavity diameter resulted in larger squish velocity and actual swirl ratio. Top clearance had little effect on flow field. Swirl is more shifted to the outward radial direction in expansion stroke as nominal swirl ratio decreases. Higher nominal swirl ratio resulted in larger actual swirl ratio, while it had little effect on squish velocity.

In-cylinder Flow Field in a Spark-ignited Natural Gas Engine. 1st Report, In-cylinder Flow Visualization by PTV.

In-cylinder flow field in a spark-ignited natural gas engine was investigated by the laser light sheet PTV method, which can analyze flow field in a short time. Using a single-cylinder visualization engine, flow field was measured right below and 10 mm, 20 mm, and 40 mm below cylinder head, at various crank angles in intake, compression, and expansion strokes. The results showed that induction-generated swirl was getting concentric to the cylinder center in compression stroke, and was shifted to the outward radial direction in expansion stroke. Swirl velocity increases with the lapse of time, showing its maximum around 20° BTDC during compression stroke, and varies from cycle to cycle within ±5% to its maximum velocity. Squish velocity shows its inward maximum and outward maximum around 20° BTDC and 20° ATDC, respectively, and varies from cycle to cycle within ±8% to its maximum outward velocity. The maximum outward squish velocity in expansion stroke is about twice as large as the maximum inward squish velocity in compression stroke.

9733288 Experimental analysis of in-cylinder combustion in a spark-ignited natural gas engine (Effect of combustion chamber configuration on in-cylinder combustion) Yukiyoshi Fukano, Haruo Hisaki, Shigeo Kida (Osaka Gas Co., Ltd.), Toshikazu Kadota (Osaka Prefecture University)

9733288 Experimental analysis of in-cylinder combustion in a spark-ignited natural gas engine (Effect of combustion chamber configuration on in-cylinder combustion) Yukiyoshi Fukano, Haruo Hisaki, Shigeo Kida (Osaka Gas Co., Ltd.), Toshikazu Kadota (Osaka Prefecture University)

Development of a natural gas spark ignition engine for optimum performance

A 4 litre displacement, six cylinder, fuel injected petrol engine was modified to natural gas (NG) fuelling. Experimental investigation was carried out with various mixture controls and compression ratios over a wide range of operating conditions. As a strategy for combustion chamber shape modification, the compression ratio was raised with simultaneous enhancement of in-cylinder turbulence through squish motion. A fast burning chamber for the combustion of lean mixtures of natural gas and air was developed. Brake thermal efficiency in excess of 40 per cent and brake torque in excess of the peak base torque with petrol were achieved. The research provides the foundation for the implementation of NG cars that will emit only about 65 per cent of the carbon dioxide (CO2) of their petrol engine counterparts, with the prospect of extending the limited range of NG cars by up to one-third and producing low hydrocarbon (HC) and nitrogen oxide (NOx) emissions.

Combustion stabilization of a spark ignition natural gas engine

Natural gas is very different from liquid fuels, such as gasoline and diesel fuel, in ignition characteristics, mixture formation process, combustion speed and so on. These characteristics greatly influence the cycle variation in the engine. The influence on lean-burn combustion is larger than that on stoichiometric combustion and the influence has not yet been sufficiently studied. In this paper, several factors for the stabilization of combustion of spark ignition natural gas lean-burn engines are clarified by means of experimental investigations using such parameters as ignition condition, swirl and compression ratio.

Heavy-Duty Spark Ignition Engines Fueled With Methane

Pollution reduction in urban areas is a major driving force to upgrade mass transportation systems. Options to the urban planner include electric traction and combustion engine upgrade. Electric traction centralizes the emission source, usually removed from urban areas, but requires substantial capital costs and lead time for the transportation infrastructure. Engine emission improvement is possible through both fuel changes and engine upgrade. Natural gas engines are a viable option for clean-operating urban buses. In the near term, conversion of existing diesel bus engines to spark-ignited natural gas is an attractive solution in terms of capital costs and lead time. This paper contains the analysis required to transform diesel engines into spark-ignited natural gas engines. Experimental data are shown for both a turbocharged and a naturally aspirated conversion. Emission data are presented showing the natural gas conversion to meet present EEC emission requirements.

A Natural Gas Engine Combustion Rig With High-Speed Photography

Engines today must satisfy stringent emission requirements but must at the same time have low fuel consumption. One method of approaching both of these goals in spark-ignited natural gas engines is with lean combustion. The use of as much as 80 percent excess air significantly reduces the peak combustion temperature and, as compared to a stoichiometric engine, reduces the NOx emissions by up to 90 percent and the fuel consumption by up to 15 percent. One limitation on lean combustion, however, is the high energy needed for ignition. In larger engines, a small prechamber containing an easily ignitable near-stoichiometric mixture has proved to be both successful and popular as one method of producing the necessary high ignition energy. Although this form of stratified charge combustion has been known for many years, its development has largely been the result of “cut and try” procedures. Lack of access for suitable instrumentation, combined with the difficulty of isolating the individual variables which affect performance, has limited the fundamental understanding of the mechanism of prechamber combustion. This paper summarizes results from a research program where a constant-volume combustion rig is used to simulate engine operation. Emphasis is placed on high-speed photography of the prechamber combustion. A second program on a single-cylinder prechamber spark-ignited gas engine and a third on a multiple-cylinder engine will be reported in subsequent papers.

Turbulence and turbulent combustion in spark-ignition engines

Nowadays, the carbon-free policies and the crisis of crude oil make natural gas get increasing attention. However, spark-ignited natural gas engines continually suffer from problems of thermal efficiency and NOx emissions. Optimizing intake and combustion systems are effective ways to improve combustion and emission performance, but comprehensive work involving both intake and combustion systems is still lacking, especially for heavy-duty commercial engines. In this work, both intake and combustion systems of spark-ignited heavy-duty natural gas engines were investigated using muti-dimensional numerical simulations. Two intake ports and four combustion chambers were considered. An optimized chemical model was employed to accelerate the computation efficiency of combustion processes. The optimal combination of intake and combustion systems was obtained, with impressive thermal efficiency and acceptable emission performance. The results show that the mixed-flow intake port performs better than the swirl intake port for the natural gas engine with premixed combustion mode, manifesting increased in-cylinder tumble ratio and turbulent kinetic energy. Meanwhile, the eccentric hemispherical combustion chamber (EHCC) combined with mixed-flow intake ports presents the best optimal combustion performance, exhibiting an effective thermal efficiency beyond 41.53%. However, the EHCC scheme shows an increased NOx emission due to fast combustion speed and high combustion temperature while negligible CO and CH4 emissions. Despite this, natural gas engines equipped with three-way catalysis after-treatment can still meet emission regulations under stoichiometric operating conditions.