Louis Sileghem

Experimental Investigation of a DISI Production Engine Fuelled with Methanol, Ethanol, Butanol and ISO-Stoichiometric Alcohol Blends

Stricter CO2 and emissions regulations are pushing spark ignition engines more and more towards downsizing, enabled through direct injection and turbocharging. The advantages which come with direct injection, such as increased charge density and an elevated knock resistance, are even more pronounced when using low carbon number alcohols instead of gasoline. This is mainly due to the higher heat of vaporization and the lower air-to-fuel ratio of light alcohols such as methanol, ethanol and butanol. These alcohols are also attractive alternatives to gasoline because they can be produced from renewable resources. Because they are liquid, they can be easily stored in a vehicle. In this respect, the performance and engine-out emissions (NOx, CO, HC and PM) of methanol, ethanol and butanol were examined on a 4 cylinder 2.4 DI production engine and are compared with those on neat gasoline. Additionally, measurements were done for E85 and a methanol-gasoline blend with the same air-to-fuel ratio as E85 because this ‘iso-stoichiometric’ methanol-gasoline blend shows very few differences in physical properties to E85 and has the potential to be used as ‘drop-in’ fuel for flex-fuel vehicles. It is shown that the brake thermal efficiency when running on alcohol fuels is significantly better than with gasoline while emitting fewer emissions. In a knock limited case for gasoline, the brake thermal efficiency on methanol was more than 5 percentage points better than on gasoline. The engine test results also confirm that, from an engine control point of view, the ‘iso-stoichiometric’ methanol-gasoline blend can indeed be used as a ‘drop-in’ fuel for E85.

Applying Design of Experiments to Determine the Effect of Gas Properties on In-Cylinder Heat Flux in a Motored SI Engine

Models for the convective heat transfer from the combustion gases to the walls inside a spark ignition engine are an important keystone in the simulation tools which are being developed to aid engine optimization. The existing models have, however, been cited to be inaccurate for hydrogen, one of the alternative fuels currently investigated. One possible explanation for this inaccuracy is that the models do not adequately capture the effect of the gas properties. These have never been varied in a wide range because air and ‘classical’ fossil fuels have similar values, but they are significantly different in the case of hydrogen. As a first step towards a fuel independent heat transfer model, we have investigated the effect of the gas properties on the heat flux in a spark ignition engine. The effect of the gas properties was decoupled from that of combustion, by injecting different inert gases (helium, argon, carbon dioxide) into the intake air flow of the engine under motored operation. This paper presents the results of the experiment, which was designed with DoE techniques. The paper shows that the three investigated effects (throttle position, compression ratio and gas) and the interaction between the throttle and the compression ratio are significant with a significance level of 1%. Both the individual and combined effects of the gas properties are investigated. The most remarkable effect observed in the data was that the dynamic viscosity influences the heat flux in two contrasting ways. At the one hand, it increases the heat flux by increasing the gas temperature, at the other hand, it reduces the heat flux through the convection coefficient. A preliminary test shows that modeling under motored operation could be based on classical concepts. However, some scatter occurs in the data which needs further investigation.

Alcohol fuels for spark-ignition engines : performance, efficiency and emission effects at mid to high blend rates for binary mixtures and pure components

The paper evaluates the results of tests performed using mid- and high-level blends of the low-carbon alcohols, methanol and ethanol, in admixture with gasoline, conducted in a variety of test engines to investigate octane response, efficiency and exhaust emissions, including those for particulate matter. In addition, pure alcohols are tested in two of the engines, to show the maximum response that can be expected in terms of knock limit and efficiency as a result of the beneficial properties of the two alcohols investigated. All of the test work has been conducted with blending of the alcohols and gasoline taking place outside the combustion system, that is, the two components are mixed homogeneously before introduction to the fuel system, and so the results represent what would happen if the alcohols were introduced into the fuel pool through a conventional single-fuel-pump (dispenser) approach. While much has been written on the effect of blending the light alcohols with gasoline in this way, the results present significant new findings with regard to the effect of the enthalpy of vaporization of the alcohols in terms of particulate exhaust emissions. Also, in one of the tests, two mid-level blends are tested in a highly downsized prototype engine – these blends being matched for stoichiometry, enthalpy of vaporization and volumetric energy content. The consequences of this are discussed and the results show that this approach to blend formulation creates fuels which behave in the same manner in a given combustion system; the reasons for this are discussed. One set of tests using pure methanol alternately with cooled exhaust gas recirculation and with excess air shows a significant increase in thermal efficiency that can be expected as the blend level is increased. The effect on nitrous oxide emissions is shown to be similarly beneficial, this being primarily a result of the enthalpy of vaporization of the alcohol cooling the charge coupled with the lower adiabatic flame temperature of the alcohol. Whereas it is normally a beneficial characteristic in spark-ignition combustion systems, one disadvantage of a high value of enthalpy of vaporization is shown in another series of tests in that, in admixture with gasoline, it is a driver on flash boiling of the hydrocarbon component in the blend in direct injection combustion systems. In turn, this causes the particulate emissions of the engine to increase quite markedly over those of ethanol–gasoline blends at the same stoichiometry. The paper shows for the first time the dichotomy of the potential efficiency improvement with the challenge of particulate control. This effect poses a challenge for the future introduction and use of such high blend rate fuels in engines without particulate filters. Although it must be stated that the overall particulate emissions of the methanol–gasoline blend are lower than for gasoline, the effect is only present at extremely low load, and that there is a likelihood that particulate filters will be adopted in production vehicle anyway, nullifying this issue.

Evolutionary decarbonization of transport: a contiguous roadmap to affordable mobility using sustainable organic fuels for transport

The paper discusses the use of methanol as a key enabler of the pragmatic, affordable and utter decarbonization of transportation. The ease with which it can be synthesized from carbonaceous feed stocks provides a contiguous route to a transportation system which can ultimately eliminate fossil-sourced CO 2. The recycling of water and CO2 to provide the hydrogen, carbon and oxygen feed stocks required has the potential to provide full energy security and to ensure the continued affordability of personal transportation. Simultaneously, the use of this methanol in methanol-to-gasoline, -diesel and kerosene processes to synthesize drop-in fuels that can fully decarbonize all forms of transport without the need for the vehicles to change significantly is shown. It is pointed out that this is the only practical means to fully decarbonize aviation. The paper is divided into several parts. Firstly a background to the desirability of methanol as a liquid transport fuel is provided, followed by a discussion of the process employed in a self-contained demonstration plant which uses air-captured CO2 (and hydrogen obtained from water electrolysis) to produce methanol and gasoline as carbon-neutral electrofuels. How methanol can gradually be introduced into current-technology and widely-affordable flex-fuel vehicles is then discussed. Some results from engines operating on pure methanol are presented, which illustrate that such engines can have higher thermal efficiencies than diesel engines. How the taxation system can be used to assist attainment of the decarbonization of transport, while still maintaining overall taxation revenue, is then discussed. Finally, a roadmap to the eventual decarbonization of all transport sectors via higher blend rates of methanol in gasoline is then outlined, eventually bringing pure methanol to forecourts for use in engines and fuel cells.

A quasi-dimensional combustion model for spark ignition engines fueled with gasoline–methanol blends:

The current work provides a quasi-dimensional model for the combustion of methanol–gasoline blends. New correlations for the laminar burning velocity of gasoline and methanol are developed and used together with a mixing rule to calculate the laminar burning velocity of the blends. Several factors (such as the laminar burning velocity, initial flame kernel, residual gas fraction, turbulence, etc.) have been investigated and the sensitivity of these factors and the used sub-models on the predictive performance was assessed. The simulation results were compared with measurement data from two engines on different gasoline–methanol blends. The results show the importance of the laminar burning velocity correlation, the method of initializing combustion and the turbulent burning velocity model. The newly developed laminar burning velocity correlation of gasoline performed equally or better than the existing correlations and the newly developed correlation of methanol outperformed the other correlations. The initial flame kernel size had a strong influence on the ignition delay. Changing the initial flame kernel to reproduce the same ignition delay was very effective to improve the simulations. Several turbulent combustion models were tested with the newly developed laminar burning velocity correlations and optimized ignition delay. In conclusion, the model of Bradley reproduced the trend going from gasoline to methanol much better than others due to the inclusion of the Lewis number.

Applying Design of Experiments to Develop a Fuel Independent Heat Transfer Model for Spark Ignition Engines

Models for the convective heat transfer from the combustion gases to the walls inside a spark ignition engine are an important keystone in the simulation tools which are being developed to aid engine optimization. The existing models are, however, inaccurate for an alternative fuel like hydrogen. This could be caused by an inaccurate prediction of the effect of the gas properties. These have never been varied in a wide range before, because air and ‘classical’ fossil fuels have similar values, but they are significantly different in the case of hydrogen. We have investigated the effect of the gas properties on the heat flux in a spark ignition engine by injecting different inert gases under motored operation and by using different alternative fuels under fired operation. Design of Experiments has been applied to vary the engine factors in a systematic way over the entire parameter space and to determine the minimum required amount of combinations. This paper presents the validation of a heat transfer model based on the Reynolds analogy for the entire experimental dataset. The paper demonstrates that the heat flux can be accurately predicted during the compression stroke with a constant characteristic length and velocity, if appropriate polynomials for the gas properties are used. Furthermore, it shows that a two-zone combustion model needs to be used as a first step to capture the effect of the flame propagation. However, alternative characteristic lengths and velocities will need to be investigated to capture the intensified convective heat transfer caused by the propagating flame front and to accurately predict the heat flux during the expansion stroke.

Development and Validation of a Quasi-Dimensional Model for (M)Ethanol-Fuelled SI Engines

Methanol and ethanol are interesting spark ignition engine fuels, both from a production and an end-use point of view. Despite promising experimental results, the full potential of these fuels remain to be explored. In this respect, quasi-dimensional engine simulation codes are especially useful as they allow cheap and fast optimization of engines. The aim of the current work was to develop and validate such a model for methanol-fuelled engines. Several laminar burning velocity correlations and turbulent burning velocity models were implemented in a QD code and their predictive performance was assessed for a wide range of engine operating conditions. The effects of compression ratio and ignition timing on the in-cylinder combustion were well reproduced irrespective of the employed u l correlation or u te model. However, to predict the effect of changes in mixture composition, the correlation and model selection proved crucial. Compared to existing correlations, a new correlation developed by the current authors led to better reproduction of the effects of equivalence ratio and residual gas content and the combustion duration. For the turbulent burning velocity, the models of Damkohler and Peters consistently underestimated the influence of equivalence ratio and residual gas content on the combustion duration, while the Gulder, Leeds, Zimont and Fractals model corresponded well with the experiments. The combination of one of these models with the new u l correlation can be used with confidence to simulate the performance and efficiency of methanol-fuelled engines.