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In this work, the effects of engine operational parameters, λ, spark timing, and compression ratio, on knock tendency and intensity as well as H2 supplementation are studied. We postulated, verified and eventually used the duration from ignition to 70% mass fraction burnt (MFB0-70%) as an explanatory variable to describe the knock tendency and intensity. In this manner, the physical factors and fuel factors that are introduced by the differences in test conditions can be differentiated. Practically, in terms of percentage of knocking cycles or the spark timing at audible knock, knock tendency decreases as λ increases and increases with H2 supplementation. However, when MFB duration is taken into account, then for the same MFB duration, knock tendency increases as λ increases and decreases with H2 supplementation.

It is established that spark ignition (SI) engines are a contributor to polycyclic aromatic hydrocarbons (PAH) in the atmosphere. Studies have shown that the PAH emissions from SI engines are dependent on fuel chemistry. In addition, a few previous studies have shown that the PAH emissions are also dependent on operating conditions. Those studies however, did not involve a wide range of operating conditions such as spark timing, engine speed and compression ratio. This paper presents experimental results of PAH emissions from a single cylinder SI engine (Ricardo E6 engine) at various operating conditions employing contemporary PAH sampling and analysis techniques. Results show that PAH emissions increase with increasing equivalence ratio, spark advance, increase in engine load and with increase in compression ratio. With the engine speed, however, the PAH emissions show a sharp decrease and then a slight increase in the emissions as the speed is increased.

Gasoline blended with kerosene, which is considered to be ‘adulterated’ fuel in South Asian countries, has been shown to increase knocking tendency in spark-ignition engines. The current study involves the use of known gasoline-kerosene blends to fuel a single cylinder Ricardo E6 engine and characterize the knocking of such blends. This paper presents results and discusses the variation of knock limited spark timing with change in kerosene proportion in the blend and with air-fuel ratio. Knock characterization is quantitatively evaluated by applying Fast Fourier Transform (FFT) and bandpass filtering techniques to the cylinder pressure data. Knock intensity of the gasoline-kerosene blends with varying proportion of kerosene is compared. An increasing amount of kerosene in the blends has been shown to increase both the knocking tendency as well as the intensity of knock.

Global ethanol trade is forecast to increase 25-fold by 2020. Most of it will be blended with gasoline to make biofuel. However, blending ethanol with gasoline has a profound effect on the evaporation characteristics of the mixture. In particular, the thermodynamic properties of the blends can be significantly different than the constituents. A clear understanding of the blend's properties is essential for optimizing engine design, e.g. utilizing charge cooling effect. Data available in the literature is very limited, considering ethanol-gasoline blends will be used as a fuel in large scale worldwide. In this work, comprehensive measurements of vapor pressures were carried out. The enthalpies of vaporization were derived from vapor pressure data using the Clausius-Clapeyron equation. Maximum vapor pressure occurs with 20% ethanol-gasoline blend at which a positive azeotrope is formed. The trend is different in enthalpy of vaporization.

Research on the combustion and performance of dual fuel stationary engines using natural gas and methane is found to be adequate in published literature. The emissions aspects, however, are less well investigated. Inadequacy is also noted in the case of published research works on biogas in dual fuel engines in respect of regulated emissions. One important pollutant which has not received much attention among researchers is the particulate matter (PM) for such applications. Though it is often claimed that PM emissions from gas-diesel dual fuel engines are much reduced, few works have been published to support this claim. The present study is intended to help fill the gap and all the regulated emissions (CO, CO2, NOx, UHC) including PM are measured for a Lister Petter direct injection stationary diesel engine modified for dual fuel applications. Two alternative gaseous fuels used in this study are natural gas and biogas.

Exhaust gas temperatures in a 1.4 L, sparked ignition engine have been measured using fine wire thermocouples at different loads and speeds. However the thermocouples are not fast enough to resolve the rapid change in exhaust temperature. This paper discusses a new thermocouple compensation technique to resolve the cycle-by-cycle variations in exhaust temperature by segmentation. Simulation results show that the technique can find the lower time constants during blowdown, reducing the bias from 28 to 4%. Several estimators and model structures have been compared. The best one is the difference equation-least squares technique, which has the combined error between -4.4 to 7.6% at 60 dB signal-to-noise ratio. The compensated temperatures have been compared against combustion parameters on a cycle-by-cycle basis. The results show that the cycle-by-cycle variations of the exhaust temperatures and combustion are correlated.

To investigate the combustion stability in a natural gas engine at idle, the burn parameters are determined on a cycle-by-cycle basis through the analysis of the engine pressure data. Combustion analysis based on cylinder-pressure provides a mechanism through which a combustion researcher can understand the combustion process. The parameters lowest normalized value (LNV) introduced by Hoard and Rehagen and coefficient of variation (COV) are used to investigate the combustion stability at idle. Measurements of combustion pressure are used to determine values for these parameters in a Ricardo research engine. The fuel used natural gas, and compression ratios between 6 and 14 are explored. The objective of this work is to identify whether these variables are a significant source of cycle-by-cycle combustion variability in a natural gas engine at idle.

The performance and combustion characteristics of a miniature two-stroke, glow ignition engine are investigated. The objective of the work is to determine the effects of three independent variables, namely: the proportion of nitromethane in the fuel, glow plug rating (‘cold’, ‘medium’ and ‘hot’), and air/fuel ratio, in order to improve understanding of the engine performance and combustion processes. Analysis of the data has shown that all of the parameters varied have an important effect on the performance and combustion characteristics of the engine.

Close control of air-fuel ratio is vital to attaining optimum performance from internal combustion engines. To ensure that air-fuel ratio is maintained at the correct value, an accurate measurement of the real-time air-fuel ratio is required. This paper investigates the use of an optical method to measure air-fuel ratio of a high performance two-stroke engine. The technique measures the light emission from the combustion process at two wavelengths, corresponding to the CH and C2 radicals. A relationship between characteristics of this light emission and air-fuel ratio has been developed over a range of engine operating conditions. Other factors that affect this relationship have also been quantified.

A thermodynamic model of spark ignition engine combustion, with multiple burned gas zones, has been extended to permit the different burned gas zones to have different mixture strengths. The NO formation is predicted in each burned gas zone using the extended Zeldovich mechanism. The model has been used to study stratified charge spark ignition engine combustion, in order to investigate the influence of overall equivalence ratio and degree of stratification on the NO emissions and the engine brake specific fuel consumption. For fixed throttle operation, it is concluded that the best trade-off is with an overall weak mixture that is close to homogeneous. For maximum power output using a slightly rich of stoichiometric mixture, then the mixture should also be close to homogeneous.

This paper describes how an optical method has been used to investigate aspects of combustion in a high performance two-stroke engine. The method involves measurement of the intensity of the light emitted at two wavelengths corresponding to the CH and C2 radicals created in the combustion process on a cycle by cycle basis. The effect of engine operating variables such as ignition timing and air-fuel ratio on the combustion light emission were examined. Comparisons are presented between the combustion light intensity measurements and conventional cylinder pressure based combustion analysis techniques. Characteristics of the light emitted by these radicals are shown to be strongly related to cylinder pressure and air-fuel ratio.

A light scattering photometer has been used to measure the diesel particulate emission from a vehicle to assess the capability of this instrument by comparing with the results from the traditional filter collection method and also with an opacimeter. Tests were conducted on a diesel vehicle mounted on a chassis dynamometer with its exhaust directed to a double dilution tunnel. Different types of test were carried out, including steady speed tests at different engine loads and transient tests. It was found that the correlation between the average particulate mass concentrations determined from the photometer and the filters changed with engine operating conditions. Comparison between the real-time outputs from the photometer and the opacimeter showed an excellent agreement in their particulate emission patterns measured during the transient tests. In conclusion, the photometer demonstrates a good potential in its application to diesel particulate measurements.

This paper investigates a technique of calculating the completeness of combustion on a cycle-by-cycle basis. The technique introduces the normalized pressure rise due to combustion parameter (Ψ) to describe the completeness of combustion. This parameter is based on the Rassweiler and Withrow method of calculating mass fraction burned and is derived from the pressure-crank angle record of the engine. Experimental data were obtained from a Rover K4 optical access engine and analyzed with a combustion analysis package. A computer simulation was then used to model the data on a cyclic basis, both with and without the completeness of combustion parameter. The inclusion of completeness of combustion improved the simulation's ability to model the experimental data both in a statistical sense (COV of IMEP) and on a cycle-by-cycle basis.

A recently suggested technique of combustion analysis has been applied to experimental data from a spark ignition engine operated at different compression ratios and over a range of spark timing and air-fuel ratio. The results of the analysis show that compression ratio has a strong effect on incompleteness of combustion and that this is detected both from unburned hydrocarbon emissions and from the new analysis method. The use of the analysis technique may give useful insights into the proportion of unburnt hydrocarbon sourced from incomplete combustion associated with cycle-by-cycle combustion variability and that sourced from crevices and other quench regions.