Search Results

Ethanol fuel blends with gasoline for spark ignition (SI) internal combustion engines are widely used on account of their advantages in terms of fuel economy and emissions reduction potential. The focus of this paper is to study the effects of these blends on combustion characteristics such as in-cylinder pressure profiles, gas-phase emissions (e.g., unburned hydrocarbons, NOx) and particulates (e.g., particulate matter and particle number) using both measurement campaigns and digital engineering workflows. Nineteen load-speed operating points in a 1L 3-cylinder GDI SI engine were measured and modelled. The measurements for in-cylinder pressure and emissions were repeated at each operating point for three types of fuel: gasoline (E0, 0% by volume of ethanol blend), E10 (10 % by volume of ethanol blend) and E20 (20% by volume of ethanol blend).

Homogeneous Charge Compression Ignition (HCCI) has emerged as a promising technology for reduction of exhaust emissions and improvement of fuel economy of internal combustion engines. There are generally two proposed methods of realizing the HCCI operation. The first is through the control of gas temperature in the cylinder and the second is through the control of chemical reactivity of the fuel and air mixture. EGR trapping, i.e., recycling a large quantity of hot burned gases by using special valve-train events (e.g. negative valve overlap), seems to be practical for many engine configurations and can be combined with any of the other HCCI enabling technologies. While this method has been widely researched, it is understood that the operating window of the HCCI engine with negative valve overlap is constrained, and the upper and lower load boundaries are greatly affected by the in-cylinder temperature.

There is an increasing recognition of injector deposit (ID) formation in fuel injection equipment as direct injection spark ignition (DISI) engine technologies advance to meet increasingly stringent emission legislation and fuel economy requirements. While it is known that the phenomena of ID in DISI engines can be influenced by changes in fuel composition, including increasing usage of aliphatic alcohols and additive chemistries to enhance fuel performance, there is however still a great deal of uncertainty regarding the physical and chemical structure of these deposits, and the mechanisms of deposit formation. In this study, a mechanical cracking sample preparation technique was developed to assess the deposits across DISI injectors fuelled with gasoline and blends of 85% ethanol (E85).

The effects of variable intake-valve-timing on the gas exchange process and performance of a 4-valve direct-injection HCCI engine were computationally investigated using a 1D gas dynamics engine cycle simulation code. A non-typical strategy to actuate the pair of intake valves was examined; whereby each valve was assumed to be actuated independently at different timing. Using such an intake valves strategy, the obtained results showed a considerable improvement of the engine parameters such as load and charging efficiency as compared with the typical identical intake valve pair timings case. Additional benefits of minimizing pumping losses and improving the fuel economy were demonstrated with the use of the non-simultaneous actuation of the intake valve pair having the opening timing of the early intake valve coupled with a symmetric degree of crank angle for the timing of exhaust valve closing.

The main obstacle for the development of Homogeneous Charge Compression Ignition (HCCI) engines is the control of auto-ignition timing, and one key is to control the trapped gas temperature so as to enable the autoignition at the end of compression stroke. Using special valve mechanisms, very high residual gas mass fraction can be achieved to raise the charge temperature. Gas exchange process hence plays a crucial role in such HCCI engines because of its strong interaction with combustion. The modification of the gas exchange process in a 4-stroke automotive engine for HCCI combustion is not straightforward, since the engine must be able to operate across a considerably wide range of speeds and loads. Intake air temperatures and the valve mechanism need to be controlled in order to deliver optimal engine performance and fuel economy. This paper presents a modelling study of the combustion and gas exchange in a HCCI engine.

A single zone combustion model based on a chemical kinetic solver has been combined with a one-dimension thermo/gas dynamic engine simulation code to study the operating characteristics of a V6 engine in which Homogeneous Charge Compression Ignition (HCCI) operation (also referred to as ‘Controlled Auto-ignition” CAI) is enabled by a cam profile switching (CPS) system with negative valve overlap. An operational window within which HCCI combustion is possible has been identified and the limit of HCCI operating region for varied valve lift possibilities is explored. The mechanisms and potential fuel economy improvements within the HCCI envelope are studied and modelled results compared against data from similar engines. It is shown that for the best fuel economy the valve timing strategy needs to be selected very carefully, despite the engine's capability to operate at a range of valve timing combinations.

The demand for more efficient and clean engines have prompted the research and development of new engine technologies. Automotive engines expected to run with leaner mixtures and higher compression ratios. Lean burn is effective to increase fuel economy whilst reducing emissions but unreliable ignition of the lean mixtures by the conventional spark plug is one of the problems which causes concerns to the engine designers. Laser ignition is a promising technology and holds many benefits over the spark ignition because it can extend the ignitability of lean mixtures with flexibility of the ignition location and absence of electrode degradation for improved engine performance with lean burn. In this study, high-speed photography is used to investigate the flame kernel growth and propagation in an optical direct injection engine using laser ignition by an Nd:YAG laser.

For Homogeneous Charge Compression Ignition (HCCI) combustion, the auto-ignition process is very sensitive to in-cylinder conditions. This includes the change in in-cylinder temperature, the composition of chemical components and their concentrations. This sensitivity presents a major challenge for the accurate control of reliable and efficient HCCI combustion. This paper outlines our recent work: 1. a real-time control oriented gasoline-fueled HCCI combustion model and its implementation in Simulink with fixed step for the conversion into dSPACE Hardware-in-the-Loop (HIL) simulation purpose. 2. The development of model-based fast calibration for the best fuel efficiency and hydrocarbon emissions via evolutionary algorithm (EA). The model reported in this paper is able to run in real-time cycle-to-cycle under engine speeds below 4000rpm and with fixed simulation steps.

Ambient temperature has significant impact on engine start ability and cold start emissions from diesel engines. These cold start emissions are accounted for substantial amount of the overall regulatory driving cycle emissions like NEDC or FTP. It is likely to implement the low temperature emissions tests for diesel vehicles, which is currently applicable only for gasoline vehicles. This paper investigates the potential of the intake heating strategy on reducing the driving cycle emissions from the latest generation of turbocharged common rail direct injection diesel engines at low ambient temperature conditions. For this investigation an air heater was installed upstream of the intake manifold and New European Driving Cycle (NEDC) tests were conducted at -7°C ambient temperature conditions for the different intake air temperatures. Intake air heating reduced the cranking time and improved the fuel economy at low ambient temperatures.

In the automotive industry, engine downsizing has been widely accepted as an enabler to improving the fuel economy and reducing the CO₂ emissions. The Atkinson cycle is one of the key technologies. In this paper, the Atkinson cycle with different expansion ratios are compared and analyzed. The investigation is compared with the benchmark whose expansion and compression ratio are identical. The aim is to understand the inherent characteristics of the over-expansion and its effect on the engine performance and emissions. The simulation results show that, the Atkinson cycle produces higher efficiency due to over-expansion. The Atkinson cycle has higher internal EGR compared with the benchmark at equivalent conditions, which contributes to lower the NOx and CO emissions.

While Homogeneous Charge Compression Ignition (HCCI) is a promising combustion mode with significant advantages in fuel economy improvement and emission reductions for vehicle engines, it is subject to a number of limitations, for example, hardware and control complexity, or NOx and NVH deterioration near its operating upper load boundary, diminishing its advantages. Conventional spark-ignition combustion mode is required for higher loads and speeds, thus the operating conditions near the HCCI boundaries and their corresponding alternatives in SI mode must be studied carefully in order to identify practical strategies to minimise the impact of the combustion mode transition on the performance of the engine. This paper presents the results of an investigation of the combustion mode transitions between SI and HCCI, using a combination of an engine cycle simulation code with a chemical kinetics based HCCI combustion code.

This paper focuses on supercharged HCCI engines employing internal EGR that is obtained by the use of negative valve overlap. In HCCI engines, the absence of throttling coupled with the use of high compression ratio to facilitate auto-ignition and with the use of lean mixtures result in improved fuel efficiency. High dilution is required to control the auto-ignition and it also results in reduction of the production of NOx. To compensate for the charge dilution effect, the method used to recover the loss of power is to introduce more air in to the engine which allows introducing also more fuel while maintaining high lambda. A supercharger is required to introduce the required amount of air into the engine. The modelling investigation performed with Ricardo WAVE® coupled with CHEMKIN® and experimental investigation for supercharged HCCI show significant improvement in terms of extension of load range and reduction of NOx over the naturally aspirated HCCI and also over SI operation.

Liquefied alternative fuels offer great potential benefits in reducing exhaust emissions and improving fuel economy of automotive engines. In order to achieve the best performance of the engine running with such fuels, it is critical to have an appropriate fuel system. In the present work, a new electronically controlled common-rail injection system has been specially designed and tested for the direct injection of liquefied alternative fuels, since a conventional pump-line-injector injection system in the conventional diesel engine was not suitable for the purpose. Experimental work has been carried out to examine and improve matching of the fuel injection system on a new fuel injection pump test bench. The preliminary engine bench test has demonstrated that this arrangement meets the requirement for the operating characteristics of a fuel injection system in a direct injection diesel engine operating with dimethyl ether (DME).