• Energy Research

Abstract Requirements of recycling low temperature waste heat energy from internal combustion engines drive the developments of excellent performance expanders with high compactness which significantly affects the applications of waste heat recovery systems to on-road vehicles. In the present study, an opposed rotary piston expander was proposed for the practical utilisations on a small-scale Organic Rankine Cycle (ORC) system, aiming at recycling the waste heat energy from internal combustion engines of on-road vehicles. The opposed rotary piston expander had a cyclic period of 180° crank angle (CA), four intake ports and two discharge ports. In order to investigate the expander performance, 3D numerical simulations were conducted under various scenarios whose boundary conditions were among the frequently reported thermodynamic states in ORC systems; additionally, these scenarios were around the design operation point of the expander. Intake and discharge characteristics, in-cylinder pressure evolutions, in-cylinder fluid flow, and P-V diagrams were analysed; further, volumetric efficiency, power output and adiabatic efficiency were calculated using the simulation results, and were compared to various types of expanders. Each two opposed cylinders had the same evolutions of cylinder volume, fluid mass, in-cylinder pressure, and temperature during operation. Maximum fluid flow rate in the intake process increased with intake pressure and rotation speed; in addition, the in-cylinder pressure reached the maximum value in a short time after the intake ports opened. However, high rotation speed also led to a drop of in-cylinder pressure (expansion process), volumetric efficiency, and adiabatic efficiency compared to low speed condition.

Abstract Popularisations of hybrid vehicles and range extender electric vehicles promote the development of high power density and small scale internal combustion engines. Opposed rotary piston (ORP) engines characterised by compact designs, few moving parts and high power density are an ideal power source for the above mentioned vehicles. Due to the short cyclic period of the ORP engine, hydrogen fuel was applied to decrease the combustion duration. This paper investigated the in-cylinder combustion and emissions characteristics of the hydrogen fuelled ORP engine using 3D numerical simulation method at various engine speeds and full load conditions. In-cylinder pressure evolutions, heat release rates, nitrogen monoxide (NO) formations, and power density were analysed to evaluate the engine performance. The results indicated that volumetric efficiency of this ORP engine was higher than 88.3% for all the given scenarios, being benefited from large area of intake ports. Peak in-cylinder pressure decreased significantly with engine speeds, which was mainly resulted from low fuel mass burn fraction before top dead centre (TDC) for high engine speed conditions. As long as the combustion chambers passed TDC, combustion flame propagated from the bowls into the gaps between end faces of adjacent pistons rapidly. In the exhaust stroke, free discharge process of this ORP engine lasted longer duration than reciprocating engines, which would lead to more energy losses. NO was mainly formed after TDC, with the accumulated NO mass being in the range of 0.07 mg–0.5 mg per cycle per cylinder in the engine speed range of 1000–5000 r/min. Maximum power density and NO emissions factor of this engine fuelled with hydrogen was approximately 69.2 kW·L−1 and 10.60 g·(kW·h)−1, respectively. Indicated thermal efficiency dropped from 36.2% to 26.5% when the engine speed increased from 1000 to 5000 r/min.

In this paper, the relationship between the operation management and fuel consumption of a coach fleet was studied. The box diagram method was used to remove the abnormal data and improve the quality of sample data. Multiple stepwise regression analysis was used to confirm the major influencing factors for fuel consumption of the coach fleet. For the selected coach fleet company, the passenger quantity fluctuated periodically in the course of a year, and the time of the lowest passenger quantity appeared during the Chinese New Year. Fuel consumption per unit turnover ( ) increased with the increase of the rated engine power in general. Fuel consumption increased and decreased with the increase of carrying mileage and turnover. According to the fluctuation of passenger quantity, the number of operation vehicles was adjusted and part of the route was rearranged. The improvement measures increased the actual loading rate and reduced fuel consumption considerably, which verified the effectiveness of the measures.

Abstract Two general methods to start the engine are investigated by the linear electric machine operating as a linear motor and identified one for a specific FPEG prototype configuration. Based on that, a novel method to start the engine by mechanical resonance is proposed. Both simulation and test results are presented, and the numerical model is successfully validated. The results show that with a fixed motor force of 110 N, within 0.5 s, the maximum in-cylinder pressure could reach 13 bar, indicating that the engine is ready for ignition. Further investigation on the engine performance with the closed-loop control strategy is carried out. The results demonstrate that it is feasible to start the FPEG with mechanical resonance with a closed-loop controlled electric linear machine that applies a proper constant motor force in the direction of the natural bouncing motion. With different starting motor force, the top dead centre (TDC) value for both cylinder is different during the first few running cycles, but the difference reduces and tends to be zero during the stable resonance state. There is not any significant difference observed on the engine frequency and piston profile during combustion process.

Abstract Hydrogen fuel applications in internal combustion engines have attracted increasing attention due to zero carbon emission and excellent combustion characteristics in terms of thermal efficiency. Internal combustion engines fuelled with hydrogen are demonstrated to have higher brake thermal efficiency than other fossil fuel cases. However, abnormal combustion such as backfire in port hydrogen injection engines limits the improvement of internal combustion engine performance resulting from low ignition energy and high flame propagation velocity of hydrogen fuel. Volumetric efficiency drops significantly if backfire occurs; moreover, it brings about damages to the intake systems and fuel injection systems. Backfire is induced by high temperature residual exhaust gas, hot spots, and abnormal discharge of spark plugs; all the factors causing pre-ignition of hydrogen-air mixture promote the backfire occurrences. This paper reviews the factors tending to induce backfire, such as improper intake valve timing and fuel injection timing, and high fuel-air equivalence ratios; additionally, the corresponding backfire control strategies are analyzed with advantages and disadvantages being discussed. The factors leading to backfire are mainly caused by large amounts of residual exhaust gas, extremely slow combustion, and improper hydrogen distributions around intake valve seats. Backfire control strategies have specific application conditions to ensure their effectiveness, beyond which they will generate negative impacts on backfire control effectiveness. Power loss is nearly inevitable for naturally aspirated engines when backfire control strategies are adopted. Multiple control strategies are recommended to ease the engine performance drop caused by backfire control; meantime, multi-objective optimizations are suggested to achieve the optimal global performance.

Abstract This paper presents the long-term effects of plastic pyrolysis oil (PPO) in a diesel engine when it is used as a primary fuel. Our previous investigation indicated that PPO is a promising fuel; however, the results suggested that the addition of diesel is necessary in order to obtain acceptable engine performance. In the present work, a blend of 75% PPO and 25% diesel was utilized in the engine for the longevity test. The engine failed after 36 hours on PPO blend when a piston was cracked. The engine’s combustion, performance and emissions characteristics were monitored throughout the longevity test revealing that the engine performance deteriorated dramatically the last hours of operation. Moreover, the analysis of the exhaust temperatures during the failure moment suggested that the underpinning reason for the cracked piston was the injector failure. After the failure, the engine was opened and the engine’s parts were investigated showing excessive wear. The lubricant oil was analysed and confirmed the increased wear due to the elevated contamination. Finally, the deposits from the piston heads were collected and analysed revealing that incomplete combustion was taking place.

Conventional diesel fuelled Partially-Premixed Compression Ignition (PPCI) engines have been investigated by many researchers previously. However, the ease of ignition and difficulty of vaporization of diesel fuel make it imperfect for PPCI combustion. In this study, Dieseline (blending of diesel and gasoline) was looked into as the Partially-Premixed Compression Ignition fuel for its combination of two fuel properties, ignition-delay-increasing characteristics and higher volatility, which make it more suitable for PPCI combustion compared to neat diesel. A series of tests were carried out on a Euro IV light-duty common-rail diesel engine, and different engine modes, from low speed/load to middle speed/load were all tested, under which fuel blend ratios, EGR rates, injection timings and quantities were varied. The emissions, fuel consumption and combustion stability of this dieseline-fuelled PPCI combustion were all investigated. The results showed that dieseline had great advantages as a PPCI combustion fuel in terms of emission reduction. This was particularly significant at high-speed engine mode. It was also found that with a blend of 50% gasoline in diesel, the particle numbers total concentration could be reduced by 90% while low NOx level and high brake fuel conversion efficiency (around 30%) were maintained at all the loads tested. © 2011 SAE International.

AbstractThe paper presents an attempt to enhance unit performance of an existing 1274 m3/h Multi Stage Flash (MSF) desalination plant through sensible heat recovery from hot distillate water at the MSF stages to warm up the make-up seawater using internal heat exchange. The extraction of the distillate from stages could increase water production by 2% and reduces steam consumption by 5%. In addition, a reduction of seawater feed flow which also results in a drop of pump power consumption were observed. Environmentally, the modification could decrease CO2 emissions by 2300 tonnes annually.

Abstract This paper presents a theoretical calculation and a preliminary design of a thermal storage system (TSS) for a heavy duty diesel engine, in order to re-utilise the wasted heat from the engine when in operation and reduce the warm-up time, thus reducing the engine emissions and improve the performance. The thermal storage mainly comprises of a heat exchanger filled with phase change material. A group of candidate materials were evaluated and NaOH H2O was selected for the particular application, as its phase change temperature is suitable and latent heat is relatively high. The storage was preliminarily designed considering the size of the engine and the quantity of heat requested, and the improvement of the engine was evaluated. The theoretical calculation suggested that nearly 40% improvement in warm-up time could be achieved with the TSS.