2B.3 - Free Piston Engine Hydraulic Pump

Transcription

1 2B.3 - Free Piston Engine Hydraulic Pump Georgia Institute of Technology Milwaukee School of Engineering North Carolina A&T State University Purdue University University of Illinois, Urbana-Champaign University of Minnesota Vanderbilt University Chen Zhang Prof. Zongxuan Sun University of Minnesota

2 Outline Introduction Previous Achievements Progresses in this year Continuous combustion tests with supercharge Trajectory effects on emissions performance Next steps 2

3 Project Summary 2B.3 Hydraulic Free Piston Engine Pump Supply fluid power (10kW-500kW) in an efficient and compact manner for mobile applications including both on-highway and off-highway vehicles with hydraulic free piston engine It will address two transformational barriers as outlined in the ERC strategic plan: compact power supply and compact energy storage. It will directly support the test bed: hydraulic hybrid passenger vehicle and it is also applicable to the excavator test bed. 3

4 Background and Motivation In fluid power systems, the current practice for generating high pressure fluid onboard is to use crankshaft based gasoline or diesel engine with a rotational hydraulic pump. Is it possible to significantly improve the efficiency of both the ICE and the pump? Hydraulic free-piston engine with advanced combustion: leverage the high efficiency of advanced combustion and the power density of hydraulic system. Crankshaft Based ICE Rotational Hydraulic Pump Current fluid power generating unit for mobile applications 4

5 Advantages of FPE Check Valves Inner Piston Pair On-off Valve LP Servo Valve Opposed Piston Opposed Cylinder (OPOC) Design Direct Injection Uniflow scavenging Intake Ports Exhaust Ports Hydraulic Chambers Outer Piston Pair Exhaust Ports On-off Valve HP Intake Ports Variable compression ratio Advanced combustion strategy Multi-fuel operation Reduced frictional losses Higher power density Internally balanced Modularity 5

6 Previously on 2B.3 System Modeling Combustion model Hydraulic model Gas dynamics Piston dynamics Hardware improvement Sensor identification Sensor calibration Pre-charge system Lubrication system DAQ and control system Moog valve and Lee valves Ignition control Fuel Injection Implementation of Advanced Control Virtual Crankshaft design Engine motoring tests Engine combustion tests The developed robust repetitive controller acts as a virtual crankshaft that would force the piston to follow the reference signal through the hydraulic actuator. Engine start Misfire recover Real time frequency and compression ratio control 6

7 Experiment Set-up and Subsystems 7

8 Achievements in the last year Upgrade of the FPE subsystems High pressure fuel injection system Boost the injection pressure to 1500 psi Reduce the fuel injection duration significantly Improve the air fuel mixing to benefit the combustion afterwards. Supercharge system Assist the mechanical scavenging pump to further boost the intake pressure Ensure sufficient fresh air blowing into the combustion chamber. Improvements on virtual crankshaft Feedforward control Further improve the tracking performance of the virtual crankshaft Transient control Eliminate the transient performance within an engine cycle Maintain appropriate TDC location in each cycle to realize continuous combustion performance. Continuous combustion test 8

9 Supercharge system for the FPE Air tank Pressure regulator Intake manifold Gas filter 9

10 Intake charge pressure comparison x 106 pos intake press inj Pa Time[s] With supercharge system, intake charge pressure is around 35 psi (2.5 bar) pos intake press inj Time[s] Without supercharge system, intake charge pressure is around 21 psi (1.5 bar) 10

11 Improvements on the virtual crankshaft: Transient control Transition when switch from motoring to firing Piston motion after applying the transient control 11

12 Continuous combustion test without supercharge system Multiple combustions are achieved. Virtual crankshaft is able to maintain engine operation even with large cycle-to-cycle combustion variation What is the reason caused this cycle-to-cycle variation and how to deal with it? (Top to bottom): Piston motion, combustion chamber pressure, heat release rate and control signal 12

13 Continuous combustion test with supercharge system Each fuel injection causes a strong combustion occurrence Supercharge system forces sufficient fresh air flowing into the combustion cylinder. Virtual crankshaft mechanism with the transient control is able to realize the continuous combustion performance in the HFPE. (Top to bottom): Piston motion, combustion chamber pressure, heat release rate and control signal 13

14 Trajectory-based combustion control Conventional ICE Fuel Economy + Emissions Free Piston Engine Valve Timing Fuel Injection Spark Timing Valve Timing Fuel Injection Spark Timing Piston Trajecotry Cycle-to-cycle discrete control Limited effects on engine cycle performance Only apply to a specific fuel Continuous in-cycle control Affect the processes prior, during and after combustion Apply to any types of fuel (alternative fuels) 14

15 Trajectory-based combustion control Pressure Temperature Species Concentration Chemical Kinetics Gas Dynamics Thermal Energy Reaction Rate Reaction Products Volume Virtual crankshaft Piston Trajectory 15

16 Trajectory effects on engine efficiency Efficiency gain achieved by HFPE Temperature profiles under extremely fuel-lean condition (AFR = 30) Higher efficiency is achieved in HFPE due to less heat loss. HFPE has the capability of igniting extremely lean fuel. 16

17 Trajectory effects on emissions Characteristics of the piston trajectories: 1. Fixed CR and fixed frequency. 2. Compressions are the same. 3. The shape of each trajectory is changed after TDC point, which means each trajectory has different expansion process. 4. Compression trajectories are determined to ensure the combustion occurs at the TDC point and expansion processes are designed to reduce NOx emission. Due to the ultimate freedom of trajectory movement, this asymmetric trajectory can be easily achieved in the HFPE with the virtual crankshaft mechanism. 17

18 Trajectory effects on emissions Temperature profiles along three trajectories NOx emissions along three trajectories Trajectory Indicated efficiency NOx emission [ppm] Blue 52.89% 504 Green 53.47% 339 Red 53.84%

19 Trajectory effect on emissions NOx productions The dominant reaction for NOx production: (based on Zeldovich Mechanism) O + N2 => NOx + N d[ NOx] dt K [ O] [ N 2 ] K exp[ 38000/ T] 2 factors affect NOx production rate: Reaction rate constant K. Species concentrations [O], [N2]. 19

20 Trajectory effect on the emissions production The dominant reaction for NOx production: (based on Zeldovich Mechanism) O + N2 => NOx + N d[ NOx] dt K [ O] [ N 2 ] 2 factors affect NOx production rate: Reaction rate constant K. Species concentrations [O], [N2]. Species amount / Volume Piston trajectory causes important influences on the emissions production. 20

21 Free Piston Engine Hydraulic Pump Project Goal: Supply fluid power in an efficient and compact manner for mobile applications. Two transformational barriers are addressed: compact power supply and energy storage It directly support two test beds: hydraulic hybrid passenger vehicle and the excavator test bed. It is the first time to achieve continuous combustion performance in the hydraulic FPE with the similar architecture. Major Objectives/Deliverables Task 1: Trajectory-based combustion control development Investigation on the trajectory effects on the engine performance Optimization of the HFPE piston trajectory Task 2: Enhancement of HFPE system capability Installation and testing of the supercharge system Installation of the necessary sensor to quantify the engine efficiency Task 3: Optimization of HFPE performance for different mobile applications Progress The tracking performance of the virtual crankshaft is improved by adding feedforward control and transient control method. The installed supercharge system improves the combustion performance. The investigation of trajectory-based combustion control demonstrates that both engine efficiency and emissions are enhanced by applying the optimal piston trajectory into the HFPE. Next Steps Achieving the optimal piston trajectory based on various loading conditions and chemical kinetics of utilized fuels. Continuously improve engine combustion performance and test virtual crankshaft at different loading conditions. 21