dadasracecar
Member
So I've been thinking about this for some time and got bored and wrote up my thoughts. I'm now considering trying to get it published as an SAE paper. What do yo guys think?
On tuning the Mazdaspeed 2.3L DISI turbocharged MZR motor
Abstract: Reasons for leaning the air fuel ratio of the 2.3L DISI turbocharged MZR motor to levels at or above 12:1 are given. These include basic theory of direct injection, observation of fuel dilution in crankcase oil, collection of fuel and water in an installed catch can, observation of impellor deterioration in the exhaust side of the turbocharger, and one example of catastrophic failure with a vented but not evacuated crankcase.
Discussion: Gasoline direct injection (GDI) engines introduce fuel directly into the cylinder as a finely atomized spray that evaporates and mixes with air to form a premixed charge of air and vaporized fuel prior to ignition. Contemporary GDI engines require high fuel pressures to atomize the fuel spray. GDI engines operate with stratified charge at part load to reduce the pumping losses inherent in conventional indirect injected engines. A stratified-charge, spark-ignited engine has the potential for burning lean mixtures for improved fuel economy and reduced emissions. Preferably an overall lean mixture is formed in the combustion chamber, but is controlled to be stoichiometric or slightly fuel-rich in the vicinity of the spark plug at the time of ignition. The stoichiometric portion is thus easily ignited, and this in turn ignites the remaining lean mixture. While pumping losses can be reduced, the operating window currently achievable for stratified charge is limited to low engine speeds and relatively light engine loads.
The Mazdaspeed 2.3L direct injection spark ignition (DISI) turbocharged MZR four cylinder motor is supplied in three vehicles, the MazdaSpeed6, MS6; the MazdaSpeed3, MS3; and the CX-7. Other popular applications of turbocharged GDI engines are the BMW 335i, the 135i, and the Audi/VW 2.0 FSI. With ever increasing emissions requirements and fuel prices driving improved fuel efficiency as a market force, more and more manufacturers are turning to forced inducted direct injection technologies to meet the demands for power and fuel efficiency.
The MS3 and MS6 are very popular with car enthusiasts bent on increasing the power delivery by modifying various parts of the engine. Popular modifications are cold air intakes, higher flowing exhausts systems, downpipes, upgraded top mount intercoolers, front mount intercoolers, exhaust manifolds, upgraded cam driven fuel pumps, and higher volume turbochargers. Interceptor type engine managements systems are often employed with the goal of optimizing the power from the stock setup and any modifications. This is especially true for the MazdaSpeed vehicles as currently there are no systems capable of reprogramming the ECU. There are several systems available using varying degrees of complexity to intercept and modify mass airflow sensor (MAF) volatage, the cam position sensor, the manifold absolute pressure (MAP) sensor, the wastegate solenoid, etc. but the method for tuning, or modifying the air fuel ratio is essentially the same, i.e. modifying the signal from the MAF. What is unclear is what the properly tuned air fuel ratio should be. Figures 1 3 show dynamometer graphs of horsepower, torque, and important for comparison, air fuel ratios (AFR) for an unmodified or stock MS6 and a 335i. A quick perusal indicates that there is no real consensus of proper AFR among manufacturers. The MS6 is particularly rich at higher rpms while the BMW and Volkswagon vehicles are, comparing to typical port fuel injected turbocharged cars and the MS6, lean.
Figure 1. Dynomometer graph from a stock 2006 MazdaSpeed6 with a 2.3L DISI turbocharged MZR.
Figure 2. Dynomometer graph from a stock 2008 BMW 335i with a DISI Turbocharged V6.
Figure 3. Dynomometer graph for a Volkswagon Golf with a 2.0 L FSI turbocharged motor
For combustion to be chemically complete, the fuel-air mixture must be vaporized to a stoichiometric gas-phase mixture. A stoichiometric combustible mixture contains the exact quantities of oxygen and fuel required for complete combustion. The products of an ideal combustion process are water and carbon dioxide. For gasoline, this air-fuel ratio is approximately 14.7:1 by weight. A fuel-air mixture that is not completely vaporized, nor stoichiometric, can result in incomplete combustion and reduced thermal efficiency. If combustion is incomplete, some carbon is not fully oxidized, yielding carbon monoxide and unburnt hydrocarbons.
Conventional forced inducted port-fuel injected motors typically run rich mixtures with AFRs in the area of 10.0-11.0:1 under load and boost. This is done to prevent or minimize preignition leading to detonation in the cylinder due to the high pressures and temperatures associated with forced induction. Because of the inherent cooling effects of GDI it is theorized that higher compression ratios and leaner air fuel mixtures can be used under load conditions than those of conventional port-fuel systems. Examples of this are shown in figures 2 and 3. Both Volkswagen and BMW set their AFR under max load/boost to be 12.0:1 or higher.
The engineers at Mazda set the fuel system for the 2.3L DISI turbocharged MZR four cylinder vehicles to run excessively rich under load, indicated in figure 1. This is inefficient as optimum power is not made in gasoline combustion engines at AFRs below 13:1. Additionally, the excessively rich condition results in unburnt fuel leaking down the cylinder walls into the crankcase. This has been described by Sagawa et al., in SAE 2002-01-1647, "Study of Fuel Dilution in Direct Injection and Multipoint Injection Gasoline Engines. Fuel dilution reduces the lubricity of oil and will result in excessive wear, heat, and, ultimately, seizure of moving parts resulting in catastrophic failure.
The following are website links to used oil analyses performed on MS3, MS6, and CX-7 vehicles. All indicate significant reduction in viscosity in comparatively short intervals.
Quaker State 5w-30
Mazdaspeed 3 - Castrol 5w 30 - first UOA - Bob Is The Oil Guy
Penzoil Platinum 5w-30 (4,116 Miles)
PP 5W30 4,116 - Mazdaspeed 3 2.3L DISI Turbo - Bob Is The Oil Guy
http://www.bobistheoilguy.com/forums/ubbth...760&fpart=1
Quaker State Q Advanced (4,300 Miles)
06 MazdaSpeed 6 Quaker Q Advanced 5W-30 4300 miles - Bob Is The Oil Guy
http://www.bobistheoilguy.com/forums/ubbth...870&fpart=1
Mobil1 (4,848 Miles)
Mobil 1 5w-30 (4,848) - 2007 Mazdaspeed 3 (9,621) - Bob Is The Oil Guy
http://www.bobistheoilguy.com/forums/ubbth...566&fpart=1
Mobil1 (5,046 Miles)
Mobil 1/ 5046 miles /2007 Mazdaspeed3 - Bob Is The Oil Guy
http://www.bobistheoilguy.com/forums/ubbth...639&fpart=1
CX-7 Motorcraft 5w-20 4,404 Miles
2007 Mazda CX-7, 2.3L Turbo, Motorcraft 5W-20 - Bob Is The Oil Guy
http://www.bobistheoilguy.com/forums/ubbth...255&fpart=1
Mazdaspeed3 Factory Fill (1,900 Miles)
2007 Mazdaspeed 3, 2.3T DISI, OEM Fill - Bob Is The Oil Guy
http://www.bobistheoilguy.com/forums/ubbth...600&fpart=1
Figure 4 is a picture of the contents of an oil catch can installed between the intake manifold and the crankcase. Under normal operation the crankcase is under vacuum and evacuating the crankcase. These catch cans were installed to eliminate the oil sludge forming inside the intake manifold, Figure 5. Owners report watery oily residue smelling of fuel when emptying their catch cans indicating fuel leakdown on the walls of the cylinders.
Figure 4. Pictures of the contents of oil catch cans installed between the intake manifold and the crankcase on two MS6s.
Figure 5. Image of the inside of the intake manifold of an MS6. The port where the oil sludge originates is connected to the crankcase PCV valve.
Excessively rich mixtures can result in unburnt fuel and chemically reduced hydrocarbons exiting the exhaust resulting in an excessively sooty condition at the tailpipe. This particulate soot also contaminates the flow in the exhaust gas recirculation system (EGR). Figure 6 is inside the cylinder head of a Mazdaspeed6. The valves have been removed but the spark plug and injector port remain. This excessive buildup was observed in a vehicle operating under normal conditions for less than 25,000 miles and likely results from a combination of the oil sludge from fuel diluted oil and the particulate from the unburnt hydrocarbons in the EGR.
Figure 6. Cylinder head of a 2006 Mazdaspeed6.
The fuel rich exhaust will continue to combust and may actually detonate outside of the cylinder in the exhaust manifold or exhaust housing of the turbocharger. Figure 7 shows the impellor from an MS6 Borg Warner K04 turbo. Close inspection reveals areas of significant deterioration of the impellor blades in an erratic fashion. The damage is not repeated from blade to blade indicating discrete damage events affecting small areas. Also the type of damage on the blades suggests a wearing away or blowing away of material due to heat/detonation. This could only arise from unburnt fuel or partially combusted hydrocarbons passing out of the cylinder and into the turbine housing. Anecdotally, the MS6 and MS3 vehicles suffer from accelerated deterioration of turbocharger function indicated by burnt oil leaking from the turbocharger seals. This symptom may also be the result of excessive heat and/or detonation inside the turbocharger itself.
Figure 7. Exhaust turbine from a Borg-Warner K04 turbo from a 2006 MS6.
Figure 8 is a picture of the block of a Mazdaspeed 2.3L DISI turbocharged MZR four cylinder motor suffering catastrophic failure. The failure occurred under boosted acceleration after approximately 10 minutes of driving with ambient temperatures in the low 30s F. This vehicles crankcase ventilation system had been modified in that the crankcase was no longer evacuated during operation but an ambient vented catch can was installed on the crankcase side. The intake manifold was, of course, plugged. The oil catch can was vented to the atmosphere constantly so that at no time was the crankcase seeing extreme pressure. The owner reported gradually increasing knock retard readings on his scantool during normal operation after installing the catch can in the described setup. The vented, non-evacuated catch can setup was used for approximately four weeks and 1500 miles. Upon failure the owner reported that no residue of any kind was found in the catch can.
Figure 8. Engine block of a 2.3L DISI turbocharged MZR four cylinder suffering catastrophic failure.
Upon disassembly of the motor, it was discovered that the rod and piston in cylinder number 2 suffered catastrophic failure. The rod was bent in two places and failed approximately 1 inch from the piston wrist pin. The piston shattered into fragments smaller than a 1 in2. The pistons and rods in cylinders 1, 3, and 4 showed no signs of adverse operating conditions. Additionally all bearing surfaces in the rods, including those of rod #2 showed minimal wear and not discrete damage markings.
The most plausible cause for this is catastrophic detonation in cylinder #2. It is possible that the oil was continually diluted with fuel from the ineffectual catch can setup to the point of lubricity breakdown and possible ignition resulting in detonation in the crankcase or oil vapor entering the cylinder and lowering the octane rating of the mixture. Another possible scenario is that some of the buildup observed in these motors was present and broke loose entering the cylinder and began to combust elevating the temperatures in that cylinder.
In a recent article by Luttermann and Mhrle titled BMW High Precision Fuel Injection in Conjunction with Twin-Turbo Technology: a Combination for Maximum Dynamic and High Fuel Efficiency, SAE 2007-01-1560, it was revealed that the BMW fuel injection system is able to vary the fuel pressure (up to 200 bar [2900 psi; approximately 1000 psi higher pressure than the fuel delivery system in the Mazda Turbo DISI MZR] and the number of injection pulses [up to three per cycle] in order to reduce the wall wetting. This is particularly important to avoid smoke emission and oil dilution. Given this information one can postulate that Mazda overcame potential fuel heterogeneities and improper combustion of their lower pressure fuel delivery system by addition of more fuel. Consequently, this results in even more smoke (unburnt hydrocarbon particulate) and oil dilution due to fuel leak down in the cylinders.
Conclusion: Excessively rich fueling conditions result in fuel dilution of the crankcase oil as well as excessive carbon build up in the intake manifold and head. The rich fueling condition may be employed to mask problems resulting from incomplete fuel atomization at the 1700 psi fuel pressure utilized by Mazda. It seems Mazdas approach was to add more fuel while BMW increased fuel pressure. It remains to be seen what the ability of the turbocharged 2.3L DISI MZR is in terms of leaner AFRs (12:1 and higher) under boost and load.
Acknowledgments: I wish to express my deep gratitude to Jordan Gartenhaus of Custom Performance Engineering and Ron Miller for some of the data supplied and many helpful discussions. Additionally, data and photographic evidence were supplied by PT Performance and Jonathon Martin.
On tuning the Mazdaspeed 2.3L DISI turbocharged MZR motor
Abstract: Reasons for leaning the air fuel ratio of the 2.3L DISI turbocharged MZR motor to levels at or above 12:1 are given. These include basic theory of direct injection, observation of fuel dilution in crankcase oil, collection of fuel and water in an installed catch can, observation of impellor deterioration in the exhaust side of the turbocharger, and one example of catastrophic failure with a vented but not evacuated crankcase.
Discussion: Gasoline direct injection (GDI) engines introduce fuel directly into the cylinder as a finely atomized spray that evaporates and mixes with air to form a premixed charge of air and vaporized fuel prior to ignition. Contemporary GDI engines require high fuel pressures to atomize the fuel spray. GDI engines operate with stratified charge at part load to reduce the pumping losses inherent in conventional indirect injected engines. A stratified-charge, spark-ignited engine has the potential for burning lean mixtures for improved fuel economy and reduced emissions. Preferably an overall lean mixture is formed in the combustion chamber, but is controlled to be stoichiometric or slightly fuel-rich in the vicinity of the spark plug at the time of ignition. The stoichiometric portion is thus easily ignited, and this in turn ignites the remaining lean mixture. While pumping losses can be reduced, the operating window currently achievable for stratified charge is limited to low engine speeds and relatively light engine loads.
The Mazdaspeed 2.3L direct injection spark ignition (DISI) turbocharged MZR four cylinder motor is supplied in three vehicles, the MazdaSpeed6, MS6; the MazdaSpeed3, MS3; and the CX-7. Other popular applications of turbocharged GDI engines are the BMW 335i, the 135i, and the Audi/VW 2.0 FSI. With ever increasing emissions requirements and fuel prices driving improved fuel efficiency as a market force, more and more manufacturers are turning to forced inducted direct injection technologies to meet the demands for power and fuel efficiency.
The MS3 and MS6 are very popular with car enthusiasts bent on increasing the power delivery by modifying various parts of the engine. Popular modifications are cold air intakes, higher flowing exhausts systems, downpipes, upgraded top mount intercoolers, front mount intercoolers, exhaust manifolds, upgraded cam driven fuel pumps, and higher volume turbochargers. Interceptor type engine managements systems are often employed with the goal of optimizing the power from the stock setup and any modifications. This is especially true for the MazdaSpeed vehicles as currently there are no systems capable of reprogramming the ECU. There are several systems available using varying degrees of complexity to intercept and modify mass airflow sensor (MAF) volatage, the cam position sensor, the manifold absolute pressure (MAP) sensor, the wastegate solenoid, etc. but the method for tuning, or modifying the air fuel ratio is essentially the same, i.e. modifying the signal from the MAF. What is unclear is what the properly tuned air fuel ratio should be. Figures 1 3 show dynamometer graphs of horsepower, torque, and important for comparison, air fuel ratios (AFR) for an unmodified or stock MS6 and a 335i. A quick perusal indicates that there is no real consensus of proper AFR among manufacturers. The MS6 is particularly rich at higher rpms while the BMW and Volkswagon vehicles are, comparing to typical port fuel injected turbocharged cars and the MS6, lean.
Figure 1. Dynomometer graph from a stock 2006 MazdaSpeed6 with a 2.3L DISI turbocharged MZR.
Figure 2. Dynomometer graph from a stock 2008 BMW 335i with a DISI Turbocharged V6.
Figure 3. Dynomometer graph for a Volkswagon Golf with a 2.0 L FSI turbocharged motor
For combustion to be chemically complete, the fuel-air mixture must be vaporized to a stoichiometric gas-phase mixture. A stoichiometric combustible mixture contains the exact quantities of oxygen and fuel required for complete combustion. The products of an ideal combustion process are water and carbon dioxide. For gasoline, this air-fuel ratio is approximately 14.7:1 by weight. A fuel-air mixture that is not completely vaporized, nor stoichiometric, can result in incomplete combustion and reduced thermal efficiency. If combustion is incomplete, some carbon is not fully oxidized, yielding carbon monoxide and unburnt hydrocarbons.
Conventional forced inducted port-fuel injected motors typically run rich mixtures with AFRs in the area of 10.0-11.0:1 under load and boost. This is done to prevent or minimize preignition leading to detonation in the cylinder due to the high pressures and temperatures associated with forced induction. Because of the inherent cooling effects of GDI it is theorized that higher compression ratios and leaner air fuel mixtures can be used under load conditions than those of conventional port-fuel systems. Examples of this are shown in figures 2 and 3. Both Volkswagen and BMW set their AFR under max load/boost to be 12.0:1 or higher.
The engineers at Mazda set the fuel system for the 2.3L DISI turbocharged MZR four cylinder vehicles to run excessively rich under load, indicated in figure 1. This is inefficient as optimum power is not made in gasoline combustion engines at AFRs below 13:1. Additionally, the excessively rich condition results in unburnt fuel leaking down the cylinder walls into the crankcase. This has been described by Sagawa et al., in SAE 2002-01-1647, "Study of Fuel Dilution in Direct Injection and Multipoint Injection Gasoline Engines. Fuel dilution reduces the lubricity of oil and will result in excessive wear, heat, and, ultimately, seizure of moving parts resulting in catastrophic failure.
The following are website links to used oil analyses performed on MS3, MS6, and CX-7 vehicles. All indicate significant reduction in viscosity in comparatively short intervals.
Quaker State 5w-30
Mazdaspeed 3 - Castrol 5w 30 - first UOA - Bob Is The Oil Guy
Penzoil Platinum 5w-30 (4,116 Miles)
PP 5W30 4,116 - Mazdaspeed 3 2.3L DISI Turbo - Bob Is The Oil Guy
http://www.bobistheoilguy.com/forums/ubbth...760&fpart=1
Quaker State Q Advanced (4,300 Miles)
06 MazdaSpeed 6 Quaker Q Advanced 5W-30 4300 miles - Bob Is The Oil Guy
http://www.bobistheoilguy.com/forums/ubbth...870&fpart=1
Mobil1 (4,848 Miles)
Mobil 1 5w-30 (4,848) - 2007 Mazdaspeed 3 (9,621) - Bob Is The Oil Guy
http://www.bobistheoilguy.com/forums/ubbth...566&fpart=1
Mobil1 (5,046 Miles)
Mobil 1/ 5046 miles /2007 Mazdaspeed3 - Bob Is The Oil Guy
http://www.bobistheoilguy.com/forums/ubbth...639&fpart=1
CX-7 Motorcraft 5w-20 4,404 Miles
2007 Mazda CX-7, 2.3L Turbo, Motorcraft 5W-20 - Bob Is The Oil Guy
http://www.bobistheoilguy.com/forums/ubbth...255&fpart=1
Mazdaspeed3 Factory Fill (1,900 Miles)
2007 Mazdaspeed 3, 2.3T DISI, OEM Fill - Bob Is The Oil Guy
http://www.bobistheoilguy.com/forums/ubbth...600&fpart=1
Figure 4 is a picture of the contents of an oil catch can installed between the intake manifold and the crankcase. Under normal operation the crankcase is under vacuum and evacuating the crankcase. These catch cans were installed to eliminate the oil sludge forming inside the intake manifold, Figure 5. Owners report watery oily residue smelling of fuel when emptying their catch cans indicating fuel leakdown on the walls of the cylinders.
Figure 4. Pictures of the contents of oil catch cans installed between the intake manifold and the crankcase on two MS6s.
Figure 5. Image of the inside of the intake manifold of an MS6. The port where the oil sludge originates is connected to the crankcase PCV valve.
Excessively rich mixtures can result in unburnt fuel and chemically reduced hydrocarbons exiting the exhaust resulting in an excessively sooty condition at the tailpipe. This particulate soot also contaminates the flow in the exhaust gas recirculation system (EGR). Figure 6 is inside the cylinder head of a Mazdaspeed6. The valves have been removed but the spark plug and injector port remain. This excessive buildup was observed in a vehicle operating under normal conditions for less than 25,000 miles and likely results from a combination of the oil sludge from fuel diluted oil and the particulate from the unburnt hydrocarbons in the EGR.
Figure 6. Cylinder head of a 2006 Mazdaspeed6.
The fuel rich exhaust will continue to combust and may actually detonate outside of the cylinder in the exhaust manifold or exhaust housing of the turbocharger. Figure 7 shows the impellor from an MS6 Borg Warner K04 turbo. Close inspection reveals areas of significant deterioration of the impellor blades in an erratic fashion. The damage is not repeated from blade to blade indicating discrete damage events affecting small areas. Also the type of damage on the blades suggests a wearing away or blowing away of material due to heat/detonation. This could only arise from unburnt fuel or partially combusted hydrocarbons passing out of the cylinder and into the turbine housing. Anecdotally, the MS6 and MS3 vehicles suffer from accelerated deterioration of turbocharger function indicated by burnt oil leaking from the turbocharger seals. This symptom may also be the result of excessive heat and/or detonation inside the turbocharger itself.
Figure 7. Exhaust turbine from a Borg-Warner K04 turbo from a 2006 MS6.
Figure 8 is a picture of the block of a Mazdaspeed 2.3L DISI turbocharged MZR four cylinder motor suffering catastrophic failure. The failure occurred under boosted acceleration after approximately 10 minutes of driving with ambient temperatures in the low 30s F. This vehicles crankcase ventilation system had been modified in that the crankcase was no longer evacuated during operation but an ambient vented catch can was installed on the crankcase side. The intake manifold was, of course, plugged. The oil catch can was vented to the atmosphere constantly so that at no time was the crankcase seeing extreme pressure. The owner reported gradually increasing knock retard readings on his scantool during normal operation after installing the catch can in the described setup. The vented, non-evacuated catch can setup was used for approximately four weeks and 1500 miles. Upon failure the owner reported that no residue of any kind was found in the catch can.
Figure 8. Engine block of a 2.3L DISI turbocharged MZR four cylinder suffering catastrophic failure.
Upon disassembly of the motor, it was discovered that the rod and piston in cylinder number 2 suffered catastrophic failure. The rod was bent in two places and failed approximately 1 inch from the piston wrist pin. The piston shattered into fragments smaller than a 1 in2. The pistons and rods in cylinders 1, 3, and 4 showed no signs of adverse operating conditions. Additionally all bearing surfaces in the rods, including those of rod #2 showed minimal wear and not discrete damage markings.
The most plausible cause for this is catastrophic detonation in cylinder #2. It is possible that the oil was continually diluted with fuel from the ineffectual catch can setup to the point of lubricity breakdown and possible ignition resulting in detonation in the crankcase or oil vapor entering the cylinder and lowering the octane rating of the mixture. Another possible scenario is that some of the buildup observed in these motors was present and broke loose entering the cylinder and began to combust elevating the temperatures in that cylinder.
In a recent article by Luttermann and Mhrle titled BMW High Precision Fuel Injection in Conjunction with Twin-Turbo Technology: a Combination for Maximum Dynamic and High Fuel Efficiency, SAE 2007-01-1560, it was revealed that the BMW fuel injection system is able to vary the fuel pressure (up to 200 bar [2900 psi; approximately 1000 psi higher pressure than the fuel delivery system in the Mazda Turbo DISI MZR] and the number of injection pulses [up to three per cycle] in order to reduce the wall wetting. This is particularly important to avoid smoke emission and oil dilution. Given this information one can postulate that Mazda overcame potential fuel heterogeneities and improper combustion of their lower pressure fuel delivery system by addition of more fuel. Consequently, this results in even more smoke (unburnt hydrocarbon particulate) and oil dilution due to fuel leak down in the cylinders.
Conclusion: Excessively rich fueling conditions result in fuel dilution of the crankcase oil as well as excessive carbon build up in the intake manifold and head. The rich fueling condition may be employed to mask problems resulting from incomplete fuel atomization at the 1700 psi fuel pressure utilized by Mazda. It seems Mazdas approach was to add more fuel while BMW increased fuel pressure. It remains to be seen what the ability of the turbocharged 2.3L DISI MZR is in terms of leaner AFRs (12:1 and higher) under boost and load.
Acknowledgments: I wish to express my deep gratitude to Jordan Gartenhaus of Custom Performance Engineering and Ron Miller for some of the data supplied and many helpful discussions. Additionally, data and photographic evidence were supplied by PT Performance and Jonathon Martin.
