The internal combustion Rankine cycle (ICRC) engine utilizes pure oxygen as the oxidant instead of air during combustion to prevent the generation of nitrogen oxide emissions and lower the cost of CO2 recovery. To control combustion intensity and increase efficiency, water injection technology is implemented as it can increase the in-cylinder working fluid during combustion process. To further enhance the system thermal efficiency, the injected water is heated using coolant and waste heat before being directly injected into combustion chamber. The main challenge of controlling the ICRC engine is the interaction between water injection process and combustion stability. Ion current detection provides a potential solution of real-time detection of in-cylinder combustion status and water injection process simultaneously. In this paper, the characteristics of ion current signal in an ICRC engine were studied. The results indicate the ion current signal is primarily affected by the combination of trapped water vapor injected in the last cycle and in-cylinder combustion intensity. The water vapor contributes to the ionization reactions, which lead to enhanced ion current signals under water cycle. The ion current signal is capable of reflecting the operating conditions of the in-cylinder water injector. The phase of the ion current peak value has a linear relation as the water injection timing is delayed, and ion current detection technology has the potential to detect the combustion phase under different engine loads in an internal combustion Rankine cycle engine.
Internal combustion Rankine cycle (ICRC) concept implements oxy-fuel combustion, direct water injection (DWI), and waster heat recovery (WHR) into traditional Otto or diesel cycle to realize high thermal efficiency and low emission powertrain. In order to support ICRC realization, this paper is dedicated to investigate the feasibility of implementing oxy-fuel combustion into diffusion combustion which provides fundamental information for future compression ignition (CI)-ICRC engine. The prototype oxy-fuel diffusion combustion engine test bench is established based on a retrofitted diesel engine, and the O2/CO2 mixture intake system, high-pressure common rail fuel injection system, and high-performance electronic controller are designed and installed within engine test bench to investigate the combustion and emission characteristics under different intake oxygen fractions (OF), fuel injection durations, and fuel injection timing. The optimum intake OF and fuel injection strategies are acquired within the selected experimental conditions, a 41.1% brake thermal efficiency (BTE), and 1.2% coefficient of variation (CoV) is achieved utilizing 55% intake OF, 0.7 ms fuel injection duration and 352 °CA (after exchange top dead center (TDC)) fuel injection timing. The oxy-fuel diffusion combustion proved to be a feasible solution for simultaneously reduction in NOX and particulate emissions, and NOX emissions lower than 90 × 10−6 with particulate matters (PM) around 0.1 filter smoke number (FSN) is observed during engine bench testing. The result of this study provides fundamental information for future CI-ICRC prototype engine establishment and optimization, which also could be utilized as reference guidance for potential industrialization of internal combustion engine (ICE) with oxy-fuel combustion mode.
This study focused on the effects of vessel and water temperatures on direct injection in internal combustion Rankine cycle engines through experimental and numerical methods. First, a study was carried out with schlieren photography using a high-speed camera for simultaneous liquid-gas diagnoses. Water was directly injected into a constant-volume vessel that provided stable boundaries. We wrote a MATLAB program to calculate spray tip penetration and cone angle from the images. For the further extension of boundary conditions, a numerical model was established and calibrated in AVL-FIRE for the thorough analysis of injection characteristics. Both experimental and numerical results indicated that injection and vessel temperatures have different effects on spray tip penetration. An increase in injected water temperature leads to shorter spray tip penetration, while the spray tip penetration increases with increasing vessel temperature. However, increased injection and vessel temperatures can both decrease the spray cone angle. Moreover, the simulation results also suggested that heat conduction is a main factor in boosting evaporation under top dead center conditions. When the internal energy of water parcels surges, these parcels evaporate immediately. These results are helpful and crucial for internal combustion engines equipped with direct water injection technology.
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