Christopher D Bannister

Oxidative Stability of Biodiesel Fuel

Biodiesel, the fatty acid alkyl esters derived from vegetable oils, animal fats, or waste cooking oils, is an alternative to diesel fuel. One of the major technical issues with the use of biodiesel is its susceptibility to oxidation. Oxidation of biodiesel is a complex process which involves a number of mechanisms producing an array of chemical components such as aldehydes, acids, ketones, and oligomeric compounds. These components in turn increase the viscosity and deposits in the fuel beyond acceptable levels. A variety of factors affect the level of these decomposition products as well as the rate of formation and decay. These factors include the temperature, presence of light, catalytic metals in the fuel system, sump oil, or storage containers, type of biodiesel, fatty acid profile, blend level, other contaminants, and presence of antioxidants. This paper examines the relevant factors influencing the biodiesel oxidative stability, the methods used to analyse and test biodiesel oxidation, as well as the effect that oxidation has on the fuels properties.

The impact of biodiesel blend ratio on vehicle performance and emissions

Abstract Biodiesel is synthesized via the transesterification of triglycerides contained within vegetable, animal, or waste oils. First-generation biofuels are not the solution to global transport energy needs; however, biodiesel does have a role to play in reducing greenhouse gas emissions from the transport sector, so long as necessary production can be achieved in a sustainable manner without negative impact on plant and animal biodiversity. The biodiesel content within diesel sold to consumers is set to increase in the future, with implications on vehicle fuel consumption, emissions, and base engine durability. This study examines the effects of increasing the biodiesel blend ratio on the performance and emissions of a production vehicle equipped with a common-rail direct-injection diesel engine, evaluated on a chassis rolls dynamometer, at various ambient temperatures. Results obtained show that reductions in engine-out carbon monoxide and hydrocarbon emissions do not always translate to lower tailpipe emissions as reduced exhaust gas temperatures at higher blend ratios lead to reduced catalyst conversion efficiencies and higher total cycle emissions. Catalyst conversion efficiencies for carbon monoxide and hydrocarbons over the New European Drive Cycle (NEDC) are reduced by 9–19 per cent (depending on the ambient temperature) for a 50:50 blend (B50) compared with the petroleum diesel (B0) baseline. Increasing the blend ratio caused a linear decrease in the vehicles maximum tractive force. This reduction was of the order of 5 per cent for a B50 blend at low vehicle speeds and 6–10 per cent at higher speeds, which is greater than would be expected on the basis of the differences in calorific values. Over the NEDC, the fuel consumption was found to increase with increasing blend ratio.

Vehicle modal emissions measurement: techniques and issues

Abstract The measurement of vehicle modal emissions is technically challenging owing to the major issue of determining exhaust-gas mass flowrate and ensuring that it is synchronous with the corresponding ‘slug’ of gas to be measured. This is also extended to the simultaneous measurement of pre- and post-catalyst emissions to determine small passive NOx conversion efficiencies. Although only really evident for passive NOx conversion efficiencies where the magnitude of catalyst performance is low in comparison to HC and CO, a misalignment between these measuring points of between will cause the resulting NOx conversion efficiency to lie anywhere between 0 per cent and 20 per cent. Further alignment issues arise when the CO2 tracer method is used for determining exhaust-gas volume flowrates. The sensitivity of time-alignment along with techniques and associated issues concerned with modal gas-flow measurement is presented in this paper.

Optimizing the lipid profile, to produce either a palm oil or biodiesel substitute, by manipulation of the culture conditions for Rhodotorula glutinis.

Background: Lipids are an increasingly important chemical feedstock for the manufacture of biofuels, bioplastics, care products and as a food source. Developing sustainable sources of lipids, derived from oleaginous microbes, is therefore a key scientific challenge. Methodology: Design of Experiments was used to optimize the lipid production and lipid profile. Results: Here we successfully apply Design of Experiments to optimize the lipid profile in Rhodotorula glutinis to tailor the fatty acid profile. A high culture temperature and high nitrogen ratio yielded a mainly monounsaturated oil, while low temperatures and high glucose loadings gave a more saturated profile. Conclusions: On transesterification, the oil high in monounsaturated esters yielded biodiesel with fuel properties akin to rapeseed methyl ester, whereas the oil high in saturates was found to be suitable as a substitute for palm oil.

Modelling and heuristic control of a parallel hybrid electric vehicle

Hybrid electric vehicles offer the potential for fuel consumption improvements when compared with conventional vehicle powertrains. The fuel consumption benefits which can be realised when utilising the hybrid electric vehicle architecture are dependent on how much braking energy is regenerated, and how well the regenerated energy is utilised. A number of power management strategies have been proposed in literature. Owing to the prospect of real-time implementation, many of these proposals have centred on the use of heuristics. Despite the research advances made, the key challenge with heuristic strategies remains achieving reasonable fuel savings without over-depleting the battery’s state of charge at the end of the trip. In view of this challenge, this paper offers two main contributions to existing energy management literature. The first is a novel, simple but effective heuristic control strategy which employs a tuneable parameter (the percentage of the maximum motor tractive power) to decide the control sequence, such that impressive fuel savings are achieved without over-depleting the final state of charge of the battery (the battery energy). The second is the quantitative exploration of braking patterns and its impact on kinetic energy regeneration. The potential of the proposed heuristic control strategy was explored over a range of driving cycles which reflect different driving scenarios. The results from this analysis show that fuel savings of as much as 19.07% can be achieved over the Japan 10–15 driving cycle. In comparison with a suboptimal controller whose control signals were derived from dynamic programming optimal control, our proposed strategy was found to be outperforming, in that it achieved impressive real-time fuel savings without much penalty to the final state of charge of the battery. Gentle braking patterns were also found to significantly improve brake energy regeneration by the electric motor.

Quantifying the Effects of Biodiesel Blend Ratio, at Varying Ambient Temperatures, on Vehicle Performance and Emissions

A number of studies have been carried out examining the impact of biodiesel blend ratio on vehicle performance and emissions, however there is relatively little data available on the interaction between blend ratio and reduced ambient temperatures over the New European Drive Cycle (NEDC). This study examines the effects of increasing the blend ratio of Rapeseed Methyl Ester (RME) on the NEDC fuel consumption and tailpipe emissions of a vehicle equipped with a 2.0 litre common rail diesel engine, tested on a chassis dynamometer at ambient temperatures of 25, 10 & -5°C. This study found that under low temperature ambient conditions increasing blend ratios had a significant detrimental effect on vehicle particulate emissions reversing the benefits observed at higher ambient temperatures. Blend ratio was found to have minimal impact on hydrocarbon emissions regardless of ambient temperature while carbon monoxide and NOx emissions were found to increase by up to 20% and 5.5% respectively. Fuel consumption rose by 5% for a B50 blend - a larger than expected increase when considering differences in calorific values alone.

The effect of engine and transmission oil viscometrics on vehicle fuel consumption

Abstract An extensive programme of work has been undertaken to assess the potential benefits of modulating the properties of both the engine and the transmission lubricating oils to achieve lower fuel consumption. The performance of the engine lubricants was evaluated on a production diesel engine on a transient test bed. The main engine lubricating-oil viscometric properties investigated were the cold cranking shear, the kinematic viscosity at 100°C, and the high-temperature high-shear value. Up to 3.5 per cent fuel economy improvement was observed over the New European Drive Cycle (NEDC), relative to current production lubricants. A model relating the fuel consumption to the oil properties was developed and verified using an experimental programme conducted on a chassis dynamometer. In a related study, the effects of changes in the transmission lubricant properties were evaluated using a standard five-speed manual transmission fitted to a light-goods vehicle and tested on a chassis dynamometer. The lubricant was heated using an external energy source to simulate the effect of a more rapid warm-up; this reduced the viscosity of the lubricant and a fuel consumption improvement of 0.7 per cent was demonstrated over the NEDC from a 25°C start. In addition, a lower-viscosity lubricant blend was evaluated, which delivered a 1 per cent improvement in the fuel economy over the standard blend from a cold start, and a further 0.4 per cent improvement if heated.

Factors affecting the decomposition of biodiesel under simulated engine sump oil conditions

Abstract Biodiesel is a renewable fuel derived from plant, waste, or algal oils. It is synthesized by the transesterification of triglycerides with an alcohol to yield fatty acid alkyl esters. These esters are prone to oxidative deterioration, yielding a variety of products which increase the viscosity of the fuel beyond acceptable levels. A proportion of the fuel used will always find its way into the vehicles lubricating oil with dilution becoming increasingly significant on vehicles equipped with a particulate filter because late injections lead to increased wall wetting. Biodiesel will also accumulate in the lubricating oil but, unlike mineral diesel, the biodiesel will not evaporate at the normal operating temperature of the oil and will instead accumulate. As the biodiesel oxidizes within the oil, degradation products will eventually form, leading to a significant increase in the oil viscosity with a potential impact on base engine durability. This study investigates the relative effects of a number of factors likely to be relevant to biodiesel oxidation within a simulated engine lubrication oil environment. The findings of this study suggest that determining the point at which oxidation occurs is inherently difficult and the impact of various factors can vary depending on the oxidation indicator examined. The most significant factors in total oxidation were found to be the temperature and air flowrate with other factors, such as the presence of iron and pro-oxidant, having a significant impact only after initial oxidation reactions had occurred.

Further Investigations on Time-Alignment

The measurement of vehicle modal emissions is technically challenging due to the major issue of determining exhaust gas mass flow rate and ensuring that it is synchronous with the emission measurement of that corresponding slug” of exhaust gas. This is very evident when attempting to measure small passive NOx catalyst conversion efficiencies. This paper highlights alignment issues with regard to the variation of time delays associated with engine and vehicle events and the CO\d2 tracer method for determining exhaust gas flows.

Robust proportional ECMS control of a parallel hybrid electric vehicle

Improved fuel efficiency in hybrid electric vehicles requires a delicate balance between the internal combustion engine usage and battery energy, using a carefully designed energy management control algorithm. Numerous energy management strategies for hybrid electric vehicles have been proposed in literature, with many of these centered on the equivalent consumption minimisation strategy (ECMS) owing to its potential for online implementation. The key challenge with the equivalent consumption minimisation strategy lies in estimating or adapting the equivalence factor in real-time so that reasonable fuel savings are achieved without over-depleting the battery state of charge at the end of the defined driving cycle. To address the challenge, this paper proposes a novel state of charge feedback ECMS controller which simultaneously optimises and selects the adaption factors (proportional controller gain and initial equivalence factor) as single parameters which can be applied in real time, over any driving cycle. Unlike other existing state of charge feedback methods, this approach solves a conflicting multiple-objective optimisation control problem, thus ensuring that the obtained adaptation factors are optimised for robustness, charge sustenance and fuel reduction. The potential of the proposed approach was thoroughly explored over a number of legislative and real-world driving cycles with varying vehicle power requirements. The results showed that, whilst achieving fuel savings in the range of 8.40 −19.68% depending on the cycle, final battery state of charge can be optimally controlled to within ±5% of the target battery state of charge.