From 640d079ba6256121c45522e9a5fc0eef8725ff8c Mon Sep 17 00:00:00 2001
From: Sam Anthony <sam@samanthony.xyz>
Date: Sun, 2 Mar 2025 14:40:09 -0500
Subject: calculate mass flow rate at standard conditions

---
 engine.c      | 13 +++++++++++++
 engine.h      |  1 +
 test.c        |  1 +
 test.h        |  1 +
 test_engine.c | 19 +++++++++++++++++++
 unit.h        |  4 ++++
 6 files changed, 39 insertions(+)

diff --git a/engine.c b/engine.c
index d0a1b38..3e0a792 100644
--- a/engine.c
+++ b/engine.c
@@ -116,3 +116,16 @@ mass_flow_rate(const Engine *e) {
 	t = e->ambient_temperature;
 	return (p * v) / (R_AIR * t);
 }
+
+/* Mass flow rate through the engine (corrected to standard conditions). */
+MassFlowRate
+mass_flow_rate_corrected(const Engine *e) {
+	Pressure p;
+	Temperature t;
+	VolumeFlowRate v;
+
+	p = STANDARD_PRESSURE;
+	t = STANDARD_TEMPERATURE;
+	v = volume_flow_rate(e);
+	return (p * v) / (R_AIR * t);
+}
diff --git a/engine.h b/engine.h
index 92b8b68..8fb816a 100644
--- a/engine.h
+++ b/engine.h
@@ -17,3 +17,4 @@ Temperature comp_outlet_temperature(const Engine *e);
 Temperature manifold_temperature(const Engine *e);
 VolumeFlowRate volume_flow_rate(const Engine *e);
 MassFlowRate mass_flow_rate(const Engine *e);
+MassFlowRate mass_flow_rate_corrected(const Engine *e);
diff --git a/test.c b/test.c
index 460c320..11348c2 100644
--- a/test.c
+++ b/test.c
@@ -63,4 +63,5 @@ main(void) {
 	test_manifold_temperature();
 	test_volume_flow_rate();
 	test_mass_flow_rate();
+	test_mass_flow_rate_corrected();
 }
diff --git a/test.h b/test.h
index 9e127f6..1e34ece 100644
--- a/test.h
+++ b/test.h
@@ -69,3 +69,4 @@ void test_comp_outlet_temperature(void);
 void test_manifold_temperature(void);
 void test_volume_flow_rate(void);
 void test_mass_flow_rate(void);
+void test_mass_flow_rate_corrected(void);
diff --git a/test_engine.c b/test_engine.c
index 4acfa17..2ac6e6e 100644
--- a/test_engine.c
+++ b/test_engine.c
@@ -105,3 +105,22 @@ test_mass_flow_rate(void) {
 	};
 	test(mass_flow_rate(&e), kilo_per_sec(0.2214056));
 }
+
+void
+test_mass_flow_rate_corrected(void) {
+	Pressure p_ambient, p_boost, map;
+
+	p_ambient = inch_mercury(30);
+	p_boost = psi(10);
+	map = p_ambient + p_boost;
+	Engine e = {
+		.displacement = cubic_inch(250),
+		.rpm = rpm(5000),
+		.map = map,
+		.ambient_temperature = fahrenheit(70),
+		.ambient_pressure = p_ambient,
+		.ve = percent(80),
+		.comp_efficiency = percent(65),
+	};
+	test(mass_flow_rate_corrected(&e), kilo_per_sec(0.2216067));
+}
diff --git a/unit.h b/unit.h
index b189ff1..d25aff9 100644
--- a/unit.h
+++ b/unit.h
@@ -1,3 +1,7 @@
+#define STANDARD_PRESSURE millibar(1013)
+#define STANDARD_TEMPERATURE celsius(20)
+
+
 typedef double AngularSpeed;
 typedef AngularSpeed (*AngularSpeedMaker)(double);
 typedef double (*AngularSpeedReader)(AngularSpeed);
-- 
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