Search Results

In the last couple of decades, countries have enacted new laws concerning environmental pollution caused by heavy-duty commercial and passenger vehicles. This is done mainly in an effort to reduce smog and health impacts caused by the different pollutions. One of the legislated pollutions, among a wide range of regulated pollutions, is nitrogen oxides (commonly abbreviated as NOx). The SCR (Selective Catalytic Reduction) was introduced in the automotive industry to reduce NOx emissions leaving the vehicle. The basic idea is to inject a urea solution (AdBlue™) in the exhaust gas before the gas enters the catalyst. The optimal working temperature for the catalyst is somewhere in the range of 300 to 400 °C. For the reactions to occur without a catalyst, the gas temperature has to be at least 800 °C. These temperatures only occur in the engine cylinder itself, during and after the combustion.

Internal combustion engine (ICE) fuel efficiency is a balance between good indicated efficiency and mechanical efficiency. High indicated efficiency is reached with a very diluted air/fuel-mixture and high load resulting in high peak cylinder pressure (PCP). On the other hand, high mechanical efficiency is obtained with very low peak cylinder pressure as the piston rings and bearings can be made with less friction. This paper presents studies of a combustion engine which consists of a two stage compression and expansion cycle. By splitting the engine into two different cycles, high-pressure (HP) and low-pressure (LP) cycles respectively, it is possible to reach high levels of both indicated and mechanical efficiency simultaneously. The HP cycle is designed similar to today's turbo-charged diesel engine but with an even higher boost pressure, resulting in high PCP. To cope with high PCP, the engine needs to be rigid.

Gas engines (fuelled with CNG, LNG or Biogas) for generation of power and heat are, to this date, taking up larger shares of the market with respect to diesel engines. In order to meet the limit imposed by the TA-Luft regulations on stationary engines, lean combustion represents a viable solution for achieving lower emissions as well as efficiency levels comparable with diesel engines. Leaner mixtures however affect the combustion stability as the flame propagation velocity and consequently heat release rate are slowed down. As a strategy to deliver higher ignition energy, an active pre-chamber may be used. This work focuses on assessing the performance of a pre-chamber combustion configuration in a stationary heavy-duty engine for power generation, operating at different loads, air-to-fuel ratios and spark timings.

Fumigation was studied in a 12 L six-cylinder heavy-duty engine. Port-injected ethanol was ignited with a small amount of diesel injected into the cylinder. The setup left much freedom for influencing the combustion process, and the aim of this study was to find operation modes that result in a combustion resembling that of a homogeneous charge compression ignition (HCCI) engine with high efficiency and low NOx emissions. Igniting the ethanol-air mixture using direct-injected diesel has attractive properties compared to traditional HCCI operation where the ethanol is ignited by pressure alone. No preheating of the mixture is required, and the amount of diesel injected can be used to control the heat release rate. The two fuel injection systems provide a larger flexibility in extending the HCCI operating range to low and high loads. It was shown that cylinder-to-cylinder variations present a challenge for this type of combustion.

This article deals with application of turbulent jet ignition technique to heavy duty multi-cylinder natural gas engine for mobile application. Pre-chamber spark plugs are identified as a promising means of achieving turbulent jet ignition as they require minimal engine modification with respect to component packaging in cylinder head and the ignition system. Detailed experiments were performed with a 6 cylinder 9.4 liter turbo-charged engine equipped with multi-point gas injection system to compare performance and emissions characteristics of operation with pre-chamber and conventional spark plug. The results indicate that ignition capability is significantly enhanced as flame development angle and combustion duration are reduced by upto 30 % compared to those with conventional spark plugs at certain operating points.

In the automotive industry, the piezo-based in-cylinder pressure sensor is getting commercialized and used in production vehicles. For example, the pressure sensor offers the opportunity to design algorithms for estimation of engine emissions, such as soot and NO , during a combustion cycle. In this paper a zero-dimensional NO model for a diesel engine is implemented that will be used in real time. The model is based on the thermal NO formation and the Zeldovich mechanism using two non-geometrical zones: burned and unburned zone. The influence of EGR on combustion temperature was modeled using a well-known thermodynamic identity where specific heat at constant pressure is included. Specific heat will vary with temperature and the gas composition. The model was implemented in LabVIEW using tools specific for an FPGA (Field-Programmable Gate Array).

Gasoline partially premixed combustion (PPC) has the potential of high efficiency and simultaneous low soot and NOx emissions. Running the engine in PPC mode with high octane number fuels has the advantage of a longer premix period of fuel and air which reduces soot emissions. The problem is the ignitability at low load and idle operating conditions. In a previous study it was shown that it is possible to use NVO to improve combustion stability and combustion efficiency at operating conditions where available boosted air is assumed to be limited. NVO has the disadvantage of low net indicated efficiency due to heat losses from recompressions of the hot residual gases. An alternative to NVO is the rebreathing valve strategy where the exhaust valves are reopened during the intake stroke. The net indicated efficiency is expected to be higher with the rebreathing strategy but the question is if similar improvements in combustion stability can be achieved with rebreathing as with NVO.

Power supply systems play a very important role in applications of everyday life. Mainly, for low power generation, there are two ways of producing energy: electrochemical batteries and small engines. In the last few years many improvements have been carried out in order to obtain lighter batteries with longer duration but unfortunately the energy density of 1 MJ/kg seems to be an asymptotic value. If the energy source is an organic fuel with an energy density of around 29 MJ/kg and a minimum overall efficiency of only 3.5%, this device can surpass the batteries. Nowadays the most efficient combustion process is HCCI combustion which is able to combine high energy conversion efficiency and low emission levels with a very low fuel consumption. In this paper, an investigation has been carried out concerning the effects of the compression ratio on the performance and emissions of a mini, Vd = 4.11 [cm3], HCCI engine fueled with diethyl ether.

Power supply systems play a very important role in everyday life applications. There are mainly two ways of producing energy for low power generation: electrochemical batteries and small engines. In the last few years, many improvements have been carried out in order to obtain lighter batteries with longer durations but unfortunately the energy density of 1 MJ/kg seems to be an asymptotic value. An energy source constituted of an organic fuel with an energy density around 29 MJ/kg and a minimum overall efficiency of only 3.5% could surpass batteries. Nowadays, the most efficient combustion process is HCCI combustion which has the ability to combine a high energy conversion efficiency with low emission levels and a very low fuel consumption. The present paper describes an investigation carried out on a modified model airplane engine, on how a pure HCCI combustion behaves in a small volume, Vd = 4.11 cm3, at very high engine speeds (up to 17,500 [rpm]).

Nowadays the power supplying systems have a fundamental importance for all small and portable devices. For low power applications, there are two main ways for producing power: electrochemical batteries and mini engines. Even though in recent years many developments have been carried out in improving the design of batteries, the energy density of 1MJ/kg seems to be an asymptotic value. If the energy source is a hydrocarbon fuel, whose energy density is 46 MJ/kg, with an overall efficiency of only 2.5 % it is possible to surpass the electrochemical batteries. On the other hand, having a mini engine, as energy source, implies three main problems: vibrations, noise and emissions. A light (230 g) model airplane engine with a displacement volume of 4.11 cm3 and a geometrical compression ratio of 13.91 has been studied. The work carried out in this paper can be divided basically in three parts.

Urban traffic involves frequent acceleration and deceleration. During deceleration, the energy previously used to accelerate the vehicle is mainly wasted on heat generated by the friction brakes. If this energy that is wasted in traditional IC engines could be saved, the fuel economy would improve. One solution to this is a pneumatic hybrid using variable valve timing to compress air during deceleration and expand air during acceleration. The compressed air can also be utilized to supercharge the engine in order to get higher load in the first few cycles when accelerating. A Scania D12 single-cylinder diesel engine has been converted for pneumatic hybrid operation and tested in a laboratory setup. Pneumatic valve actuators have been used to make the pneumatic hybrid possible. The actuators have been mounted on top of the cylinder head of the engine. A pressure tank has been connected to one of the inlet ports and one of the inlet valves has been modified to work as a tank valve.

Nowadays for small-scale power generation there are electrochemical batteries and mini engines. Many efforts have been done for improving the power density of the batteries but unfortunately the value of 1 MJ/kg seems to be asymptotic. If the energy source is an organic fuel which has an energy density of around 29 MJ/kg with a minimum overall efficiency of only 3.5%, this device would surpass the batteries. This paper is the fifth of a series of publications aimed to study the HCCI combustion process in the milli domain at high engine speed in order to design and develop VIMPA, Vibrating Microengine for Low Power Generation and Microsystems Actuation. Previous studies ranged from general characterization of the HCCI combustion process by using metal and optical engines, to more specific topics for instance the influence of the boundary layer and quenching distance on the quality of the combustion.

Partially Premixed Combustion (PPC) is a combustion concept by which it is possible to get low smoke and NOx emissions simultaneously. PPC requires high EGR levels and injection timings sufficiently early or late to extend the ignition delay so that air and fuel mix extensively prior to combustion. This paper investigates the operating region of single injection diesel PPC in a multi cylinder heavy duty engine resembling a standard build production engine. Limits in emissions and fuel consumption are defined and the highest load that fulfills these requirements is determined. Experiments are carried out at different engine speeds and a comparison of open and closed loop combustion control are made as well as evaluation of an extended EGR-cooling system designed to reduce the EGR temperature. In this study the PPC operating range proved to be limited.

This paper offers a two-zone NOx model suitable for vehicle on-board, on-line implementation. Similar NOx modeling attempts have previously been undertaken. The hereby suggested method does however offer clear and important benefits over the previously methods, utilizing a significantly different method to handle temperature calculations within the (two) different zones avoiding iterative computation. The new method significantly improves calculation speed and, most important of all, reduces implementation complexity while still maintaining reasonable accuracy and the physical interpretation of earlier suggested methods. The equations commonly used to compute NOx emissions is also rewritten in order to suit a two-zone NOx model. An algorithm which can be used to compute NOx emissions is presented and the intended contribution of the paper is a NOx model, implementation feasible for an embedded system, e.g. embedded processor or embedded electronic hardware (FPGA).

This paper is the follow up of a previous work and its target is to demonstrate that the best fuel for a Compression Ignition engine has to be with high Octane Number. An advanced injection strategy was designed in order to run Gasoline in a CI engine. At high load it consisted in injecting 54 % of the fuel very early in the pilot and the remaining around TDC; the second injection is used as ignition trigger and an appropriate amount of cool EGR has to be used in order to avoid pre-ignition of the pilot. Substantially lower NOx, soot and specific fuel consumption were achieved at 16.56 bar gross IMEP as compared to Diesel. The pressure rise rate did not constitute any problem thanks to the stratification created by the main injection and a partial overlap between start of the combustion and main injection. Ethanol gave excellent results too; with this fuel the maximum load was limited at 14.80 bar gross IMEP because of hardware issues.

The behavior of Ethanol and seven fuels in the boiling point range of gasoline but with an Octane Number spanning from 69 to 99 was investigated in Partially Premixed Combustion. A load sweep was performed from 5 to 18 bar gross IMEP at 1300 rpm. The engine used in the experiments was a single cylinder Scania D12. To allow high load operations and achieve sufficient mixing, the compression ratio was decreased from the standard 18:1 to 14.3:1. It was shown that by using only 50% of EGR it is possible to achieve NOx below 0.30 g/kWh even at high loads. At 18 bar IMEP soot was in the range of 1-2 FSN for the gasoline fuels while it was below 0.06 FSN with Ethanol. The use of high boost combined with relatively short combustion duration allowed reaching gross indicated efficiencies in the range of 54 - 56%. At high load the partial stratified mixture allowed to keep the maximum pressure rise rate below 15 bar/CAD with most of the fuels.

In the study presented in this paper, a vehicle driving cycle simulation of the pneumatic hybrid has been conducted. The pneumatic hybrid powertrain has been modeled in GT-Power and validated against experimental data. The GT-Power engine model has been linked with a MATLAB/simulink vehicle model. The engine in question is a single-cylinder Scania D12 diesel engine, which has been converted to work as a pneumatic hybrid. The base engine model, provided by Scania, is made in GT-power and it is based on the same engine configuration as the one used in real engine testing. During pneumatic hybrid operation the engine can be used as a 2-stroke compressor for generation of compressed air during vehicle deceleration and during vehicle acceleration the engine can be operated as a 2-stroke air-motor driven by the previously stored pressurized air.

The current research focuses in understanding how inlet pressure, EGR, combustion phasing, engine speed and pilot main ratio are affecting the main parameters of the combustion (e.g. efficiency, NOx, soot, maximum pressure rise rate) in the novel concept of injecting high octane number fuels in partially premixed combustion. The influence of the above mentioned parameters was studied by performing detailed sweeps at 32 bar fuel MEP (c.a. 16-18 bar gross IMEP); three different kinds of gasoline were tested (RON: 99, 89 and 69). The experiments were ran in a single cylinder heavy duty engine; Scania D12. At the end of these sweeps the optimized settings were computed in order to understand how to achieve high efficiency, low emissions and acceptable maximum pressure rise rate.

A Scania 13 1 engine modified for single cylinder operations was run using nine fuels in the boiling point range of gasoline, but very different octane number, together with PRF20 and MK1-diesel. The eleven fuels were tested in a load sweep between 5 and 26 bar gross IMEP at 1250 rpm and also at idle (2.5 bar IMEP, 600 rpm). The boost level was proportional to the load while the inlet temperature was held constant at 303 K. For each fuel the load sweep was terminated if the ignitibility limit was reached. A lower load limit of 15 and 10 bar gross IMEP was found with fuels having an octane number range of 93-100 and 80-89 respectively, while fuels with an octane number below 70 were able to run through the whole load range including idle. A careful selection of boost pressure and EGR in the previously specified load range allowed achieving a gross indicated efficiency between 52 and 55% while NOx ranged between 0.1 and 0.5 g/kWh.

Homogeneous Charge Compression Ignition (HCCI) holds great promises for good fuel economy and low emissions of NOX and soot. The concept of HCCI is premixed combustion of a highly diluted mixture. The dilution limits the combustion temperature and thus prevents extensive NOX production. Load is controlled by altering the quality of the charge, rather than the quantity. No throttling together with a high compression ratio to facilitate auto ignition and lean mixtures results in good brake thermal efficiency. However, HCCI also presents challenges like how to control the combustion and how to achieve an acceptable load range. This work is focused on solutions to the latter problem. The high dilution required to avoid NOX production limits the mass of fuel relative to the mass of air or EGR. For a given size of the engine the only way to recover the loss of power due to dilution is to force more mass through the engine.