Lean Operating Limit Research Articles

A Numerical Study of Lean CH4/H2/Air Premixed Flames at High Pressure

We perform a numerical study of the effect of including a small amount of hydrogen in lean methane-air premixed flames at high pressure and high temperature conditions. It has been shown recently (Bell and Gupta (1997)) that hydrogen addition extends the lean operating limit of natural gas engines, leading to a potential decrease in pollutant formation. We suggest here that the origin of this effect is that, at constant global equivalence ratio, the stretch resistance of these flames is considerably increased by hydrogen blending, while other flame properties, such as ignition time and burnt gas temperature, are comparatively little modified.

A parametric study on the lean misfiring and knocking limits of gas-fueled spark ignition engines

Increasing emphasis on gaseous fuels as clean, economical and abundant fuels encourages the search for optimum operating conditions of gas-fueled internal combustion engines. In this context, this paper presents the experimental results of a parametric study on the lean operational limits of a Ricardo E6 engine using propane and liquefied petroleum gas (LPG) as fuels. Three different criteria for defining the engine lean limit are used. The first is associated with the first detectable misfire on leaning the mixture, the second is the first detectable firing under motoring conditions when the mixture is being enriched slowly, while the third is when the torque reaches zero on leaning the mixture. In addition, the lean knocking limit for some experiments is presented. The effects of speed, spark timing, compression ratio, intake temperature, intake pressure (supercharging), and relative humidity of intake air on the engine operational limits are presented and discussed in relation to chemical reaction rates, ignition delay, amount of residual gases, turbulence, and heat transfer.

Auto Ignition and Combustion of DME and n-Butane/Air Mixtures in Homogeneous Charge Compression Ignition Engine.

Auto ignition, which is observed in Homogeneous and Premixed Charge Compression Ignition engine, expand the lean flammability limit of engine operation and realize stable ignition and combustion at a range of ultra-lean conditions, where NOx emissions are reduced. In this study, we made a basic research on mechanism of auto ignition and combustion with various premixed gas temperature and compression speed on n-butane and dimethyl ether (DME). And we observed singularity phenomena appearing in auto ignition at low temperature of n-butane/air mixture in Homogeneous Charge Compression Ignition engine.

Effect of the Factors of Combustion Chamber on the Performance and Exhaust Emissions in a Natural Gas Fueled Spark Ignition Engine.

An experimental study was made on a natural gas fueled spark ignition engine to improve its thermal efficiency and exhaust emissions by the lean burn operation. A multi-cylinder engine was used to obtain the data for practical application. Investigated were the effects of the throat area of the orifice which separated a prechamber from a main chamber, the position of ignition spark in the prechamber and the compression ratio on the thermal efficiency, the exhaust emissions and the lean limit of stable operation. The results showed that a small throat area resulted in low emissions of NOx, low thermal efficiency and narrow lean limit. The spark ignition at the center of prechamber or near the throat was preferable to the top of prechamber in terms of the thermal efficiency. Higher compression ratio resulted in shorter combustion duration, higher thermal efficiency and extended lean limit.

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 with lower pollutant emissions over a relatively broad range of lean equivalence ratios; and (v) the impact of hydrogen blending on performance and emissions was dependent on the volume fraction of hydrogen, although the functional relationship appeared to be non-linear.

An Investigation of the Lean Operational Limits of Gas-Fueled Spark Ignition Engines

Examination is made of the operational limits in two variable compression-ratio single-cylinder engines when operating on the gaseous fuels methane, propane, LPG, and hydrogen under a wide range of conditions. Two definitions for the limits were employed. The first was associated with the first detectable misfire on leaning the mixture, while the second was the first detectable firing under motoring condition in the presence of a spark when the mixture was being enriched slowly. Attempts were also made to relate these limits to the corresponding values for quiescent conditions reckoned on the basis of the flammability limits evaluated at the mean temperature and pressure prevailing within the cylinder charge at the time of the spark. The measured limits in the engine were always higher than the corresponding flammability limit values for the three fuels. Both of these limits appear to correlate reasonably well with the calculated mean temperature of the mixture at the time of passing the spark.

Torch Ignition: Ideal for Lean Burn Premixed-Charge Engines

Sluggish flame initiation and propagation, and even potential misfiring, become major problems with lean-fueled, premixed-charge, spark-ignited engines. This work studies torch ignition as a means for improving combustion, fuel economy, and emissions of a retrofitted, large combustion chamber with nonideal spark plug location. A number of alternative configurations, employing different torch chamber designs, spark-plug locations, and materials, were tested under full-load and part-load conditions. Results indicate a considerable extension of the lean operating limit of the engine, especially under part-load conditions. In addition, torch ignition can lead to substantial thermal efficiency gains for either leaner or richer air-fuel ratios than the optimum for the conventional ignition system. On the richer side, in particular, the torch-ignited engine is capable of operating at maximum brake torque spark timings, rather than compromised, knock-limited spark timings used with conventional ignition. This translates into thermal efficiency improvements as high as 8 percent at an air-fuel ratio of 20:1 and full load.

Effect of Di-t-Butyl Peroxide on the Lean Operating Limit of a Spark-Ignition Engine

Abstract A study was conducted to determine whether the addition of di-t-butyl peroxide to unleaded gasoline would extend the lean operating limit of a spark-ignition engine. Tests were conducted with a single-cylinder, Cooperative Fuel Research engine. In these tests, the lean misfire limit equivalence ratio was extended by 6 and 10 percent with blends of 1 and 5 volume percent, respectively, of di-t-butyl peroxide and unleaded gasoline, compared to the value obtained with only unleaded-gasoline. It is hypothesized that the improved lean combustion was caused by the dissociation of di-t-butyl peroxide to tertiary butoxy radicals, which in turn reacted with the unleaded gasoline thus increasing the fuel oxidation rate.

Engine Induction Developments - Economic and Reduced Exhaust Emissions: Fuel Vapourization - Economy with Reduced Exhaust Emission

SYNOPSIS This paper describes a simple system of controlling exhaust emissions from gasoline engined vehicles, using a coolant-heated fuel vaporiser in the inlet system. The object of complete vaporisation of the fuel is to create a homogeneous inlet charge, giving improved cylinder-to-cylinder distribution and permitting operation with very lean mixtures. This leads to low exhaust emissions of Carbon Monoxide, Hydrocarbons and Nitric Oxides. The effects of vaporisation on the lean limit of operation, exhaust emissions, power output, fuel consumption and optimum spark ignition timing have been investigated, and are discussed in the paper. Results of tests on a 1.6 litre car are also presented. It was found that exhaust emissions were effectively controlled, while vehicle driveability remained acceptable. Engine power was reduced by 25-30%, although fuel consumption was not increased.