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Since 1st September 2014 the Hong Kong Environmental Protection Department (HKEPD) has been utilising a Dual Remote Sensing technique to monitor the emissions from gasoline and liquified petroleum gas (LPG) vehicles for identifying high emitting vehicles running on road. Remote sensing measures and determines volume ratios of the emission gases of HC, CO and NO against CO2, which are used for determining if a vehicle is a high emitter. Characterisation of each emission gas is shown and its potential to identify a high emitter is established. The data covers a total of about 2,200,000 LPG vehicle emission measurements taken from 14 different remote sensing units. It was collected from 6th January 2012 to 20th April 2017 across a period before and after the launch of the Remote Sensing programme for evaluating the performance of the programme. The results show that the HKEPD Remote Sensing programme is very effective to detect high emitting vehicles and reduce on-road vehicle emissions.

Vehicle emissions and fuel consumption are significantly affected by driving behavior. Many studies of eco-driving technology such as eco-driving training, driving simulators and on-board eco-driving devices have reported potential reductions in emissions and fuel consumption. Use of on-board safety devices is mainly for safety, but also affects vehicle emissions and fuel consumption. In this study, an on-board safety device was installed to alert the driver and provide several types of warning to the driver (e.g. headway monitoring warning, lane collision warning, speed limit warning, etc.) to improve driving behavior. A portable emissions measurement system (PEMS) was used to measure vehicle exhaust concentrations, including hydrocarbons (HC), carbon monoxide (CO), carbon dioxide (CO2) and nitrogen oxides (NOx). The driving parameters including vehicle speed, acceleration and position were also recorded.

Ethanol as a renewable fuel has been used widely in vehicles. Dual fuel injection is one of the new techniques in development for increasing the engine’s thermal efficiency and reducing the pollutant emissions. This study reports experimental investigation to the dual ethanol fuel injection with a focus on the effect of spark timing on the engine performance at different volumetric ratios of ethanol directly injected to ethanol port injected. Experiments were conducted on a single cylinder 250cc spark ignition engine at two engine loads and 3500 RPM. The spark timing was varied from 15 to 42 CAD bTDC at the light load and from 15 to 32 CAD bTDC at the medium load, while the volumetric ratio of direct injection (DI%) was varied from 0% to 100%.

Ethanol direct injection (EDI) has great potential in facilitating the downsizing technologies in spark ignition engines due to its strong anti-knock ability. The fuel temperature may vary widely from non-evaporating to flash-boiling sprays in real engine conditions. In this study, a CFD spray model was developed in the ANSYS Fluent environment, which was capable to simulate the EDI spray and evaporation characteristics under non-evaporating, transition and flash-boiling conditions. The turbulence was modelled by the realizable k-ε model. The Rinzic heterogeneous nucleation model was applied to simulate the primary breakup droplet size at the nozzle exit. The secondary breakup process was modelled by the Taylor Analogy Breakup model. The evaporation process was modelled by the Convection/Diffusion Controlled Model. The droplet distortion and drag, collision and droplet-wall interaction were also included.

Ethanol direct injection (EDI) is a new technology to use ethanol fuel more efficiently in spark ignition engines. Fuel temperature is one of the key factors which determine the evaporation process of liquid fuel spray, and consequently influence the combustion and emission generation of the engine. To better understand the mixture formation process of the EDI spray and provide experimental data for engine modelling, experiments were conducted in a constant volume chamber in engine-like conditions. The high speed Shadowgraphy imaging technique was used to capture the ethanol spray behaviours. The experiments covered a wide range of fuel temperature, ranged from 275 K (non-evaporating) to 400 K (flash-boiling). Particularly the transition of the ethanol spray from normal-evaporating to flash-boiling was investigated.

The work reported in this paper contributes to understanding the effects of ethanol/gasoline ratio on mixture formation and cooling effect which are crucial in the development of EDI+GPI engine. The spray simulations were carried out using a commercial CFD code. The model was verified by comparing the numerical and experimental results of spray shapes in a constant volume chamber and cylinder pressure in an EDI+GPI research engine. The verified model was used to investigate the fuel vaporization and mixture formation of the EDI+GPI research engine. The effect of the ethanol/gasoline ratio on charge cooling has been studied. Compared with GPI only, EDI+GPI demonstrated stronger effect on charge cooling by decreased in-cylinder temperature. However, the cooling effect was limited by the low evaporation rate of the ethanol fuel due to its lower saturation vapour pressure than gasoline's in low temperature conditions.

Premixed charge compression ignition (PCCI) is a new combustion mode to reduce NOX and soot emission. It requires the optimization of the injection timing and pressure, fuel mass in pilot injection and EGR rate. A 6-cylinder, turbocharged, common rail heavy-duty diesel engine was used in this study. The effect of multiple injection strategies on diesel fuel combustion process, heat release rate, emission and economy of diesel engine is studied. The multiple injection strategies include different EGR level, pilot injection timing, pilot injection mass and post injection timing to achieve the homogeneous compression ignition and lower temperature combustion of diesel engine. Based on endoscope technology, the two-color method was applied to take the flame images in the engine cylinder and obtain soot concentration distribution, to understand the PCCI combustion in diesel engines.

Ethanol direct injection plus gasoline port injection (EDI+GPI) is a new technology to make the use of ethanol fuel more effective and efficient in spark ignition engines. It takes the advantages of ethanol fuel, such as its greater latent heat of vaporization than that of gasoline fuel, to enhance the charge cooling effect and consequently to increase the compression ratio and improve the engine thermal efficiency. Experimental investigation has shown improvement in the performance of a single cylinder spark ignition engine equipped with EDI+GPI. It was inferred that the charge cooling enhanced by EDI played an important role. To investigate it, a CFD model has been developed for the experimentally tested engine. The Eulerian-Lagrangian approach and Discrete Droplet Model were used to model the evolution of the fuel sprays. The model was verified by comparing the numerical and experimental results of cylinder pressure during the intake and compression strokes.

Ethanol direct injection plus gasoline port injection (EDI+GPI) is a new technical approach to make the use of ethanol fuel more effective and efficient in spark ignition (SI) engines. Ethanol fuel direct injection timing, as one of the primary control parameters in EDI+GPI engines, directly affects the quality of the fuel/air mixture and consequently combustion and emissions. This paper reports the experimental investigation to the effect of ethanol injection timing and pressure on engine performance, combustion, emissions of a single cylinder SI engine equipped with EDI+GPI. Firstly, the effect of EDI timing before and after the inlet valve closing, defined as early and late injection timings (EEDI and LEDI) was investigated at three injection pressure levels of 40 Bar, 60 Bar and 90 Bar and a fixed ethanol/gasoline ratio. Spark timing was fixed at original engine setting to investigate the potential engine efficiency improvement due to the EDI solely.

Ethanol has been used either as an alternative fuel or in blends with gasoline in spark ignition (SI) engines for many years. However, the existing method of using ethanol fuel by blending gasoline and ethanol fuel does not fully exploit the ethanol fuel's potential in improving engine thermal efficiency and reducing pollutant emissions. The dual-fuel injection strategy, ethanol direct injection plus gasoline port injection (EDI+GPI), offers a potentially new way to make the best use of ethanol fuel. In this paper the potential of EDI+GPI is investigated based on experiments conducted on a single cylinder SI research engine equipped with EDI+GPI. The leveraging effect of EDI+GPI on engine performance was investigated at different ethanol/gasoline energy ratios (EERs) and speeds. Then further investigation to the leveraging effect enhanced by ethanol injection timing and spark timing was performed. Experimental results showed that the IMEP increased with the increase of EER.

In this paper, an Electronic Control System (ECS) is designed to manage a 125 cc single-cylinder air-cooled motorcycle engine. The aim of this study was to accomplish low cost, high reliability and mainly meet the motorcycle engine emission standard of China Stage III. The intake port fuel injection mode was chosen with a redesigned part of intake pipe. Gathering information of speed, throttle position (TP), inlet temperature and pressure, cylinder temperature, switch-type exhaust gas oxygen sensor and the battery voltage, an Engine Control Unit (ECU) was devised to calculate fuel injecting pulse width, advance ignition angle and control the working conditions of the fuel pump and the exhaust gas oxygen sensor. Additionally, a three-way catalytic converter (TWC) was used to reduce exhaust gas emissions.

Cyclic instability is a common problem in the operation of conventional two-stroke spark-ignition engines. Previous research has shown that auto-ignition (AI) could help solve this problem. However, at light engine loads, even under AI, the cyclic instability may still be significant due to the difficulty in maintaining the minimum temperature required by AI. Despite the benefits brought by AI in fuel consumption and emission reduction, the high level of cycle-to-cycle variation at light load may delay the realization of AI operation in engine products. To solve this problem, spark assistance has been identified as a cost effective and convenient way to improve the stability of AI operation at light load. This paper aims to report our experimental investigation to the effectiveness of spark assistance on cyclic variation of AI at light engine load conditions.

The local temperature of the in-cylinder mixture before combustion is critical to enable auto-ignition (AI) in a gasoline engine. Spark assistance is one of the methods to ensure the critical temperature required for auto-ignition. The application of the spark gives a time controlled initiation to the onset of ignition. In the work reported in this paper, spark assisted AI was experimentally investigated on a small two-stroke engine. The spark assistance and internal exhaust gas recirculation (EGR) were jointly applied to achieve and control AI. The results showed that at higher engine load, the onset timing of AI had a clear dependence on the timing of the spark and was consistent from cycle to cycle. At lower engine load, the assistance of the spark became necessary for keeping the AI operation to continue.

A 2D axissymmetric CFD model of a prototype free-piston engine has been developed using a commercial code. The dynamics of a passive inlet valve mounted on the moving piston was the main interest in the investigation. Preliminary results of cylinder and compressor pressure show good agreement with experimental pressure data for both fired and motoring conditions. Insight into the probable lift characteristics of the passive inlet valve was obtained. The CFD model achieves the simulation of complex multi-body movement through structured mesh deformation. Momentum source terms are utilized to modify flow in certain domains in the model. The paper reports the difficulty of specifying appropriate loss terms for a 2D model of 3D flow. It concludes by assessing the suitability of simplified 2D CFD to model gas dynamics. In cases where the flow departs significantly from a 2D form, either 3D CFD or 1D gas dynamics is probably a better choice.

A simple method to reduce HC emissions caused by fuel short-circuiting in a two-stroke engine is to apply a certain restriction to the exhaust gas flow in the exhaust pipe. This technique, developed for motorcycles, vehicles and outboards, has been applied to a small off-road two-stroke engine with a constant speed operating condition. In order to assess the feasibility and effectiveness of this technique for the reduction of HC and CO emissions in such an engine, a butterfly valve was installed in the exhaust pipe next to the exhaust port. Based on test results using the butterfly valve, a cylindrical restrictor was developed to generate various restrictions to the gas flow in the exhaust pipe and consequently reduce the fuel short-circuiting. The effectiveness of the restrictor on emission reduction was further improved by leaner air/fuel mixture.

Cycle-to-cycle variations occur frequently in small two-stroke engines as a result of irregular combustion and misfire due to the presence of the charge with incorrect air to fuel ratio and burnt gas adjacent to the spark plug. Under normal operating conditions burnt gasses inhibit the flame propagation that initiates from the spark plug. In this paper auto-ignition has been investigated as a means of overcoming the above problem by converting the presence of burnt gas from a disadvantage to an advantage. Under the current investigation trapping exhaust gas using a butterfly valve installed in the exhaust manifold was adopted as a method of realising auto-ignition in a small single cylinder two-stroke engine. Within the operating region of auto-ignition a significant reduction in cycle-to-cycle variations was achieved.

A 3-D CFD model for a small two-stroke SI engine has been developed using a commercial code. The model simulates the scavenging process from the exhaust port opening to closing. The fluid in this model is air only. RNG (re-normalized group) was adopted as the turbulence model. The moving piston was achieved using the deforming grid technique. Various methods for numerically visualizing the air short-circuited through the exhaust port were investigated. This paper reports the modified Janté method, particle spray and thermal images. Although the results are only qualitative identification of air short-circuiting, they show that all three methods have the potential to achieve quantitative identification of fresh charge short-circuiting.

A natural gas engine based on the principle of a long stroke reciprocating mechanism (LSRM) is proposed. The crankshaft arrangement in a conventional internal combustion (IC) engine will be replaced by a LSRM featuring long stroke and low speed. A major advantage of this LSRM system is that it considerably reduces the side force, which is inherent in conventional crankshaft arrangements. Another advantage is that the LSRM engine will be more compact than an equivalent crank engine operating under the same conditions of speed, power output and so on. The reduced size and complexity of the engine lead to a favorable reduction in manufacturing and, more importantly, maintenance costs. Using gas fuel will allow an increased compression ratio, which is usually limited by the operating nature of the Otto cycle in gasoline engines. With a longer stroke length and lower engine speed, the engine fuel injection system can achieve better engine combustion and performance than current IC engines.

The exhaust noise of a two-cylinder four-stroke diesel engine was experimentally investigated in order to examine the predictability of the exhaust noise to be reduced by a feedforward active control system. Special attention has been paid to the low frequency characteristics of the exhaust noise as low frequency noise is difficult to reduce with a conventional muffler but effective to control by active control technique. The periodicity of the exhaust noise was examined with the ensemble-average and ensemble-standard deviation of the exhaust pressure signals. The results showed that the exhaust noise investigated was basically quasi-periodic and its variation between cycles was acceptable with an adaptive control algorithm. The properties of the exhaust pressure in low frequency domain were analyzed with the spectra of the exhaust noise pressure.

This paper reports the work on modeling the exhaust noise pressure of a small single-cylinder SI engine. The model will ultimately be used for on-line prediction of exhaust noise in an active control system with a single-error microphone. The frequency properties of the engine exhaust noise generated by this SI engine are characterized by harmonic components related to engine firing conditions. The frequencies of the harmonic components depend only on the engine firing frequency while the amplitudes of the harmonic components vary with the engine load. The twenty harmonic components at the lower frequency band were used to model the exhaust pressure pulse which is a two-dimensional function of engine speed and load. The model is represented by a double Chebyshev polynomial. The instantaneous exhaust pressure at steady state for a fixed position in the exhaust pipe was predicted using this model and compared with the experimental data.