Experimental study of the performance and emissions characteristics of a small diesel genset operating in dual-fuel mode with three different primary fuels

A dual fuel engine is an internal combustion engine where the primary gaseous fuel source is pre-mixed with air as it enters the combustion chamber. This homogenous air fuel mixture is ignited by a small quantity of diesel known as the ‘pilot’ that is injected towards the end of the compression stroke. The diesel fuel ignites in the same way as in compression ignition (CI) engines, and the gaseous fuel is consumed by flame propagation in a similar manner to spark ignited engines. The motivation to dual-fuel a CI engine is partly economic due to the lower cost of the primary fuel, and partly environmental as some emissions characteristics are improved. In the present study, a direct injection four cylinder CI engine, typically used in genset applications, was fuelled with three different gaseous fuels; methane, propane and butane. The performance and emissions (NOx and smoke) characteristics of various gaseous concentrations were recorded at 1500rpm (synchronous speed) and at ¼, ½, and ¾ load. In order to invest igate the combustion performance under these different conditions, a three zone heat release rate analysis is proposed an applied to the data. The resulting mass burned rate, ignition delay and combustion duration are used to explain the emissions and performance characteristics of the engine. It will be shown that the highest gas substitution levels were achieved when using methane under all test conditions, but emissions of NOx and smoke were lower when using propane. Butane proved to be the most unsatisfactory of the three primary fuels, with the highest emissions of NOx and smoke

The effects of soot properties on the regeneration behaviour of wall-flow diesel particulate filters

In recent years, significant effort has been put into studying the regeneration process of diesel particulate filters (DPFs) either through experiments or modelling. However, less attention is paid to understanding the important influence of soot properties on the regeneration process. In this paper, for the first time, five fundamental soot properties, namely activation energy, frequency factor of the reaction, soot bulk density, porosity and mean soot particulate diameter, are investigated. Sensitivity analyses are carried out for each of these parameters based on a one-dimensional generalized DPF regeneration model. It is found that activation energy is the most important factor in the regeneration process, followed by frequency factor, bulk density, porosity and mean particulate size. In addition, the results also indicate that the concentration of exhaust gas oxygen has a significant influence on the role played by each parameter. This clearly shows the importance of gas diffusion in the regeneration process

A diesel particulate filter regeneration model with a multi-step chemical reaction scheme

Diesel particulate filters (DPFs) are considered necessary in order to meet future global diesel engine emissions legislation. Various regeneration methods have been developed to clean DPFs by periodic oxidation of trapped particulate matter (soot). To achieve this goal, it is important to understand the fundamentals of the regeneration process. Previous soot oxidation regeneration models relied on tunable chemical kinetic parameters to achieve agreement between model and experimental results. In the work reported in this paper, a multistep chemical reaction scheme is incorporated in a model to study the thermal regeneration process. The regeneration model does not require tunable parameters and its results compare well with experimental findings. The effects on regeneration of various gas species are also studied, in addition to O2 and N2, such as CO and H2O that are present in the exhaust gas. The model is also used to demonstrate the effects of quenching the regeneration process and its impact on partial filter regeneration

An experimental study into the effect of the pilot injection timing on the performance and emissions of a high-speed common-rail dual-fuel engine

Dual fuel technology has the potential to offer significant improvements in emissions of carbon dioxide from light-duty compression ignition engines. In these smaller capacity high speed engines, where the combustion event can be temporally shorter, the injection timing can have an important effect on the performance and emissions characteristics of the engine. This paper discusses the use of a 0.51-litre single-cylinder high speed direct injection diesel engine modified to achieve port directed gas injection. The effect of pilot diesel injection timing on dual fuel engine performance and emissions was investigated at engine speeds of 1500 and 2500 rpm and loads equivalent to 0.15, 0.3, 0.45 and 0.6 MPa gross indicated mean effective pressure, for a fixed gas substitution ratio (on an energy basis) of 50%. Furthermore, the effect of pilot injection quantity was investigated at a constant engine speed of 1500 rpm by completing a gaseous substitution sweep at the optimised injection timing for each load condition. The results identify the limits of single injection timing during dual fuel combustion and the gains in engine performance and stability that can be achieved through optimisation of the pilot injection timing. Furthermore, pilot injection timing and quantity were shown to have fundamental effects on the formation and emission of carbon monoxide, nitrogen oxide and total hydrocarbons. The potential for dual fuel combustion to achieve significant reductions in specific CO2 was also highlighted, with reductions of up to 30% being achieved at full load compared to the baseline diesel case

A finite-volume-based two-dimensional wall-flow diesel particulate filter regeneration model

Many existing diesel particulate filter (DPF) models do not sufficiently describe the actual physiochemical processes that occur during the regeneration process. This is due to the various assumptions made in the models. To overcome this shortcoming, a detailed twodimensional DPF regeneration model with a multistep chemical reaction scheme is presented. The model solves the variable density, multicomponent conservation equations by the pressure implicit with splitting of operators (PISO) scheme for inlet and outlet channels as well as the porous soot layer and filter wall. It includes a non-thermal equilibrium (NTE) model for the energy equation for porous media. In addition, for the first time, experiments on the DPF were conducted to determine the interstitial heat transfer coefficient inside the DPF porous wall. The results compare well with an in-house one-dimensional model and subsequently this was used in the new two-dimensional model. By using this detailed two-dimensional model, some interesting observations of the DPF regeneration process were revealed. These included flow reversals and asymmetry in the filter channels

Measurements of laminar premixed methane–air flame thickness at ambient conditions

A new experimental data set for the flame thickness of laminar premixed methane—air flames at ambient conditions is presented. Prior to combustion the temperature and pressure of the premixed mixture were 298 K>5 K and 100 kPa>5 kPa, respectively. The fuel—air equivalence ratio was varied from 0.8 to 1.4 in 0.05 steps. The data were obtained using simultaneous imaging of the visible and Schlieren cones on the central axis of the symmetrical flame front of a non-cooled burner configuration. The data were analysed and the plane obtained from the Schlieren image corrected using a one-dimensional energy balance to obtain the position of the cold surface of the flame and hence allow determination of the flame thickness. The data presented agree within experimental errors with the limited existing published data. For the range of equivalence ratios studied, a second-order equation was fitted and presented for methane—air flames at atmospheric pressure and ambient temperatures

Experimental study of DI diesel engine performance using three different biodiesel fuels

Methyl esters derived from vegetable oils by the process of transesterification (commonly referred as ‘biodiesel’), can be used as an alternative fuel in compression ignition engines. In this study, three different vegetable oils (rape, soy and waste oil) were used to produce biodiesel fuels that were then tested in a four cylinder direct injection engine, typically used in small diesel genset applications. Engine performance and emissions were recorded at five load conditions and at two different speeds. This paper presents the results obtained for measurements of NOx and smoke opacity at the different speed and load conditions for the three biodiesels, and their blends (5 and 50% v/v) with mineral diesel. A simple combustion analysis was also performed where ignition delay, position and magnitude of peak cylinder pressure and heat release rate were examined to asses how the variation of chemical structure and blend percentage affects engine performance. Engine performance and emissions for all of the 5% biodiesel blends were indistinguishable from mineral diesel. However, at higher blends, the rape fuel exhibited better emission and performance characteristics than either the soy or waste fuels. Furthermore; whilst emissions trends varied for each blend and fuel, emissions of smoke were significantly reduced at all speed and load conditions, and NOx was reduced by up to 50% at low loads. It will also be shown that while engine performance was not significantly deteriorated by biodiesel, there was evidence of increased ignition delay with higher blends, and a possible two stage ignition process where mineral diesel ignited earlier than the biodiesel